Edgar Filing: ATLANTIC POWER CORP

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TABLE OF CONTENTS
TABLE OF CONTENTS

Filed Pursuant to Rule 424(b)(5)
Registration No. 333-183135

CALCULATION OF REGISTRATION FEE

Title of Each Class of Securities to be Registered	Amount to be Registered	Proposed Maximum Offering Price Per Share(1)	Proposed Maximum Aggregate Offering Price(1)	Amount of Registration Fee(2)




Common Shares, no par value per share	5,962,443	$13.60	$81,089,224.80	$9,292.83

(1): Pursuant to Rule 457(c), based on the average of the high and low prices of the common shares on August 3, 2012, as reported on the New York Stock Exchange.
(2): Calculated in accordance with Rule 457(r) under the Securities Act of 1933, as amended (the "Securities Act"). Payment of the registration fee at the time of filing of the registrant's registration statement on Form S-3, filed with the Securities and Exchange Commission on August 8, 2012, was deferred pursuant to Rules 456(b) and 457(r) under the Securities Act, and is paid herewith. This "Calculation of Registration Fee" table shall be deemed to update the "Calculation of Registration Fee" table in such registration statement.

Prospectus Supplement
August 8, 2012
(To Prospectus dated August 8, 2012)

Dividend Reinvestment Plan

5,962,443 Common Shares

This prospectus supplement describes our Dividend Reinvestment Plan (the "Plan"). You should read this prospectus supplement carefully before you invest and retain it for future reference. Your participation in the Plan is entirely voluntary, and you may terminate your participation at any time.

The Plan enables eligible holders of our common shares to reinvest cash dividends to acquire additional common shares. Under the Plan:

•: The price at which common shares will be issued from treasury on reinvestment of cash dividends will be equal to the Average Market Price (as defined below), less a discount of 3%.
•: No commissions, service charges or brokerage fees are payable by participants in connection with the issuance of common shares from treasury under the Plan.
•: Dividends in respect of common shares purchased under the plan will be held by the plan administrator for the participants' accounts and automatically invested under the Plan in additional common shares.

We have appointed Computershare Trust Company of Canada (the "Agent") to serve as the administrator of the Plan. Any eligible registered shareholder may become a participant in the Plan at any time by completing an Enrollment Form (as defined below) online or by downloading and duly completing and signing a Reinvestment Enrollment—Participation Declaration Form (the "Enrollment Form") at www.computershare.com/investorcentrecanada and returning it to the Agent no later than 4:00 p.m. (Toronto time) on the fifth business day immediately preceding a dividend record date.

A shareholder who is a beneficial owner and not an owner of record of common shares (e.g., whose shares are held by, and registered in the name of, a bank, trust company, investment dealer or other intermediary for the account of the participant) must make arrangements with the bank, trust company, investment dealer or other intermediary through which they hold their common shares to enroll as a participant in the Plan, as described above, or will be required to transfer such common shares into his, her or its own name or into a specific segregated registered account such as a numbered account with a bank, trust company, investment dealer or other intermediary in order for that person to become a Registered Participant (as defined below).

The payment of dividends is solely at the discretion of our Board of Directors, which may not declare a dividend or may change the amount and timing of dividends at any time without notice.

Our common shares trade on the Toronto Stock Exchange (the "TSX") under the symbol "ATP" and on the New York Stock Exchange (the "NYSE") under the symbol "AT." On August 7, 2012, the last reported sale price of our common shares on the TSX and the NYSE was C$13.80 and $13.84, respectively, per share.

Investing in our securities involves risks. See "Risk Factors" on page 7 before you make your investment decision. Neither we nor the Agent can provide any assurance of a profit or protection against loss on any shares purchased under the Plan.

Neither the Securities and Exchange Commission ("SEC") nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus supplement is August 8, 2012.

Table of Contents

TABLE OF CONTENTS

		Page

About this Prospectus Supplement			S-4
Where You Can Find More Information			S-4
Our Company			S-5
Cautionary Note Regarding Forward-Looking Statements			S-6
Risk Factors			S-7
Use of Proceeds			S-8
Frequently Asked Questions			S-8
Description of the Plan			S-11
Certain Canadian Federal Income Tax Considerations			S-17
Certain United States Tax Considerations for United States Residents			S-19
Plan of Distribution			S-22
Legal Matters			S-22
Experts			S-22

You should rely only on the information provided or incorporated by reference in this prospectus supplement and accompanying prospectus. If anyone provides you with different or additional information, you should not rely on it. We have not authorized anyone to provide you with different, inconsistent or additional information. We are not making an offer to sell these securities in any jurisdiction where the offer or sale of these securities is not permitted. You should not assume that the information appearing in this prospectus supplement and accompanying prospectus or the documents incorporated by reference herein or therein is accurate as of any date other than their respective dates. Our business, financial condition, results of operations and prospects may have changed since those dates.

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About this Prospectus Supplement

This document is in two parts. The first part is the prospectus supplement, which adds to and updates information contained in the accompanying prospectus. The second part, the prospectus, provides more general information, some of which may not apply to this offering. Generally, when we refer to this prospectus, we are referring to both parts of this document combined. To the extent there is a conflict between the information contained in this prospectus supplement and the information contained in the accompanying prospectus, you should rely on the information in this prospectus supplement.

Before purchasing any securities, you should carefully read both this prospectus supplement and the accompanying prospectus, together with the incorporated documents described under the heading "Where You Can Find More Information" in this prospectus supplement and the accompanying prospectus.

As used in this prospectus supplement, the terms "Atlantic Power," the "Company," "we," "our" and "us" refer to Atlantic Power Corporation, together with those entities owned or controlled by Atlantic Power Corporation, unless the context indicates otherwise. Unless otherwise noted, all references to "C$," "Cdn$" and "Canadian dollars" are to the lawful currency of Canada and all references to "$," "US$" and "U.S. dollars" are to the lawful currency of the United States. This prospectus supplement includes our trademarks and other trade names identified herein. All other trademarks and trade names appearing in this prospectus supplement are the property of their respective holders.

Where You Can Find More Information

We file annual, quarterly and current reports, proxy statements and other information with the SEC. You may read and copy any document we file at the SEC's Public Reference Room at 100 F Street, N.E., Washington, D.C. 20549. You may call the SEC at 1-800-SEC-0330 for further information on the operation of the Public Reference Room. Our SEC filings are also available to the public from the SEC's website at http://www.sec.gov and on our website at http://www.atlanticpower.com. We have included the SEC's web address and our web address as inactive textual references only. Our website is not incorporated into, and does not constitute a part of, this prospectus supplement or any other report or documents we file with or furnish to the SEC.

The SEC allows us to incorporate by reference the information we file with it, which means that we can disclose important information to you by referring you to these documents. The information incorporated by reference is an important part of this prospectus supplement, and information that we file later with the SEC will automatically update and supersede the information already incorporated by reference. Atlantic Power's SEC file number is 001-34691. We are incorporating by reference the documents listed below, which were previously filed by us with the SEC:

•: our Annual Report on Form 10-K for the year ended December 31, 2011, filed with the SEC on February 29, 2012, as amended on April 2, 2012;
•: our Quarterly Report on Form 10-Q for the quarter ended March 31, 2012, filed with the SEC on May 7, 2012;
•: our Quarterly Report on Form 10-Q for the quarter ended June 30, 2012, filed with the SEC on August 8, 2012;
•: our annual Proxy Statement on Schedule 14A relating to our annual meeting of shareholders, filed with the SEC on April 30, 2012;

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•: our Current Reports on Form 8-K filed with the SEC on February 3, 2012, March 2, 2012, April 5, 2012, June 25, 2012, July 6, 2012 and July 16, 2012, except, in any such cases, the portions furnished and not filed pursuant to Item 7.01 or otherwise;
•: the audited consolidated financial statements of Capital Power Income L.P. and its subsidiaries as of December 31, 2010 and 2009 and for each of the three years ended December 31, 2010, 2009 and 2008, and the notes related thereto, filed as Exhibit 99.1 to our Current Report on Form 8-K/A, filed with the SEC on December 20, 2011;
•: the unaudited condensed interim consolidated financial statements of Capital Power Income L.P. and its subsidiaries as of and for the three and nine months ended September 30, 2011 and 2010 and the notes related thereto, filed as Exhibit 99.2 to our Current Report on Form 8-K/A, filed with the SEC on December 20, 2011;
•: the unaudited pro forma condensed combined consolidated statement of operations of the Company and Atlantic Power Limited Partnership for the year ended December 31, 2011 and the notes related thereto, included under the heading "Unaudited Pro Forma Condensed Consolidated Statement of Operations" in our prospectus filed with the SEC pursuant to Rule 424(b) on July 3, 2012;
•: the description of the Company's common shares contained in the Company's Registration Statement on Form 10, filed with the SEC on July 21, 2010; and
•: all documents filed by us with the SEC pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act after the date of this prospectus supplement and prior to the termination of this offering, except as to any portion of any future report or document that is not deemed filed under such provisions.

You may request a copy of these filings, and any exhibits we have specifically incorporated by reference as an exhibit in this prospectus supplement, at no cost by writing or telephoning us at the following: Atlantic Power Corporation, One Federal Street, Floor 30, Boston, Massachusetts 02110. Our telephone number is (617) 977-2400.

Our Company

Atlantic Power Corporation owns and operates a diverse fleet of power generation and infrastructure assets in the United States and Canada. Our power generation projects sell electricity to utilities and other large commercial customers largely under long-term power purchase agreements ("PPAs"), which seek to minimize exposure to changes in commodity prices. Our power generation projects in operation have an aggregate gross electric generation capacity of approximately 3,397 megawatts (or "MW") in which our aggregate ownership interest is approximately 2,141 MW. Our current portfolio consists of interests in 31 operational power generation projects across 11 states in the United States and two provinces in Canada and a 500-kilovolt 84-mile electric transmission line located in California. In addition, we have one 53 MW biomass project under construction in Georgia and one approximately 300 MW wind project under construction in Oklahoma. We also own a majority interest in Rollcast Energy Inc., a biomass power plant developer in North Carolina. Twenty-three of our projects are wholly-owned subsidiaries.

We sell the capacity and energy from our power generation projects under PPAs with a number of utilities and other parties. Under the PPAs, which have expiration dates ranging from 2012 to 2037, we receive payments for electric energy delivered to our customers (known as energy payments), in addition to payments for electric generating capacity (known as capacity payments). We also sell steam from a number of our projects to industrial purchasers under steam sales agreements. The transmission system rights associated with our power transmission project entitle us to payments indirectly from the utilities that make use of the transmission line.

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Our power generation projects generally have long-term fuel supply agreements, typically accompanied by fuel transportation arrangements. In most cases, the term of the fuel supply and transportation arrangements corresponds to the term of the relevant PPAs. Many of the PPAs and steam sales agreements provide for the indexing or pass-through of fuel costs to our customers. In cases where there is no pass-through of fuel costs, we often attempt to mitigate the market price risk of changing commodity costs through the use of financial hedging strategies.

We directly operate and maintain more than half of our power generation fleet. We also partner with recognized leaders in the independent power industry to operate and maintain our other projects, including Caithness Energy, LLC, Colorado Energy Management, Power Plant Management Services and the Western Area Power Administration. Under these operation, maintenance and management agreements, the operator is typically responsible for operations, maintenance and repair services.

Our common shares trade on the TSX under the symbol "ATP" and on the NYSE under the symbol "AT." Our 6.50% convertible secured debentures due October 31, 2014 issued pursuant to the trust indenture dated as of October 11, 2006 between us and Computershare Trust Company of Canada (the "Debenture Trustee") as supplemented by the first supplemental indenture dated as of November 27, 2009 trade on the TSX under the symbol "ATP.DB." Our 6.25% convertible unsecured subordinated debentures due March 15, 2017 issued pursuant to the trust indenture dated as of December 17, 2009 between us and the Debenture Trustee trade on the TSX under the symbol "ATP.DB.A." Our 5.60% Series B convertible unsecured subordinated debentures due June 30, 2017 issued pursuant to the trust indenture dated December 17, 2009 between us and the Debenture Trustee as supplemented by the first supplemental indenture dated October 20, 2010 trade on the TSX under the symbol "ATP.DB.B." Our 5.75% Series C convertible unsecured subordinated debentures due June 30, 2019 issued pursuant to the trust indenture dated December 17, 2009 between us and the Debenture Trustee as supplemented by the second supplemental indenture dated July 5, 2012 trade on the TSX under the symbol "ATP.DB.U." The issued and outstanding preferred shares of our indirect, wholly-owned subsidiary, Atlantic Power Preferred Equity Ltd. trade on the TSX under the symbols "AZP.PR.A" and "AZP.PR.B."

Our registered office is located at 355 Burrard Street, Suite 1900, Vancouver, British Columbia, Canada V6C 2G8 and our headquarters is located at One Federal Street, Floor 30, Boston, Massachusetts 02110 USA. Our telephone number in Boston is (617) 977-2400 and the address of our website is www.atlanticpower.com. We make available, free of charge, on our website our Annual Report on Form 10-K, Quarterly Reports on Form 10-Q, Current Reports on Form 8-K and amendments to those reports filed or furnished pursuant to Section 13(a) or 15(d) of the Exchange Act as soon as reasonably practicable after we electronically file such material with, or furnish it to, the SEC. Additionally, we make available on our website, our Canadian securities filings. Other than specific documents incorporated by reference, information on our web site is not incorporated into this prospectus supplement or our other securities filings and does not form a part of this prospectus supplement.

Cautionary Note Regarding Forward-Looking Statements

This prospectus supplement, the accompanying prospectus, the documents incorporated or deemed to be incorporated by reference in this prospectus supplement and accompanying prospectus and other written or oral statements made from time to time by the Company may contain forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995 with respect to the financial condition, results of operations, business strategies, operating efficiencies, synergies, revenue enhancements, competitive positions, plans and objectives of management and growth opportunities of Atlantic Power Corporation, and with respect to the markets for Atlantic Power common shares and other matters. Statements in this prospectus supplement and the documents incorporated by reference herein that are not historical facts are hereby identified as forward-looking statements for the purpose

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of the safe harbor provided by Section 27A of the Securities Act and Section 21E of the Exchange Act and forward-looking information within the meaning defined under applicable Canadian securities legislation (collectively, "forward-looking statements").

Forward-looking statements can generally be identified by the use of words such as "should," "intend," "may," "expect," "believe," "anticipate," "estimate," "continue," "plan," "project," "will," "could," "would," "target," "potential" and other similar expressions. In addition, any statements that refer to expectations, projections or other characterizations of future events or circumstances are forward-looking statements. Although we believe that the expectations reflected in such forward-looking statements are reasonable, such statements involve risks and uncertainties, and undue reliance should not be placed on such statements. Certain material factors or assumptions are applied in making forward-looking statements, including, but not limited to, factors and assumptions regarding the items outlined above. Actual results may differ materially from those expressed or implied in such statements. Important factors that could cause actual results to differ materially from these expectations include, among other things:

•: the amount of distributions expected to be received from our projects;
•: the ability of the Company to generate sufficient amounts of cash and cash equivalents to maintain our operations and meet obligations as they become due;
•: the expected use of proceeds from offerings of our securities;
•: the impact of legislative, regulatory, competitive and technological changes;
•: expectations regarding completion of construction of certain projects; and
•: other risk factors relating to us and the power industry, as detailed from time to time in our filings with the SEC and the Canadian Securities Administrators.

You are cautioned that any forward-looking statement speaks only as of the date of this prospectus supplement or, if such statement is included in a document incorporated by reference into this prospectus supplement, as of the date of such other document. We undertake no obligation to update or revise any forward-looking statement, whether as a result of new information, future events or otherwise, except as may be required by applicable law.

Risk Factors

Investing in our common shares involves risks. In addition to the specific risks discussed below, you should carefully consider the risks, uncertainties and additional information (i) set forth in our most recent Annual Report on Form 10-K, as amended, any subsequent Quarterly Reports on Form 10-Q and SEC reports on Form 8-K, which are incorporated, or deemed to be incorporated, by reference into this prospectus supplement and accompanying prospectus, and in the other documents incorporated by reference in this prospectus supplement and accompanying prospectus that we file with the SEC after the date of this prospectus supplement and which are deemed incorporated by reference herein. For a description of these reports and documents, and information about where you can find them, see "Where You Can Find More Information." The risks and uncertainties in the documents incorporated by reference in this prospectus supplement and accompanying prospectus are those that we currently believe may materially affect our company. Additional risks not presently known or that are currently deemed immaterial could also materially and adversely affect our financial condition, results of operations, business and prospects.

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Risks Relating to Participation in the Plan

You will not know the price of the common shares you are purchasing under the Plan at the time you authorize the investment or elect to have your dividends reinvested.

The price of our common shares may fluctuate between the time you decide to purchase shares under the Plan and the time of actual purchase. In addition, during this time period, you may become aware of additional information that might affect your investment decision, but you may not be able to change or cancel your purchase authorization.

You will not be able to direct the specific time or price at which your common shares are sold under the Plan.

You will not be able to direct the time and price at which your common shares are sold. If you decide to withdraw from the Plan, the Agent will send you a direct registration system advice or a common share certificate for whole shares credited under the Plan. If you request a common share certificate, the market price of our common shares may decline between the time you decide to withdraw and the time you receive the certificate.

Use of Proceeds

We have no basis for estimating the number of our common shares that ultimately will be purchased from us pursuant to the Plan or the prices at which such shares will be sold. The net proceeds from the sale of any authorized and unissued common shares sold pursuant to the Plan will be used by us for general corporate purposes, which may include the repayment or refinancing of outstanding indebtedness.

Frequently Asked Questions

1. What is the Plan?

The Plan is a plan that enables eligible holders of common shares of the Company to invest cash dividends, if, as and when declared and paid on common shares, to acquire additional common shares.

2. What are the advantages of participating in the Plan?

•: A participant may purchase additional common shares with the cash dividends (net of any applicable withholding taxes) paid on the common shares which are held by the participant or held in a participant's account maintained pursuant to the Plan.
•: The price at which common shares will be issued from treasury on reinvestment of cash dividends on common shares will be equal to the Average Market Price (as defined below), less a discount of 3%.
•: No commissions, service charges or brokerage fees are payable by participants in connection with the issuance of common shares from treasury to participants under the Plan.
•: Full investment of participants' funds is possible under the Plan because the Plan permits fractions of common shares as well as whole common shares to be purchased and held for participants.
•: Dividends in respect of common shares purchased under the Plan will be held by the Agent for the participants' accounts and automatically invested under the Plan in additional common shares of the Company.

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3. Who is eligible to participate in the Plan?

All holders of common shares who are Canadian or U.S. residents are eligible to participate in the Plan at any time by enrolling in the Plan as described in Question 4 below.

4. How do I enroll in the Plan?

Nearly all of our shareholders are beneficial owners, meaning that their common shares are registered in the name of their stock brokerage, financial institution or other nominee. If you're an eligible beneficial holder of common shares, you must contact your stock brokerage, financial institution or other nominee with whom your shares are held to enroll in the Plan.

If you are an eligible registered holder of common shares, you can enroll in the Plan by completing an enrollment form online through the Agent's self-service web portal, Investor Centre, at www.computershare.com/investorcentrecanada or by downloading and returning a completed and signed enrollment form to the Agent by no later than 4:00 p.m. (Toronto time) on the fifth business day immediately preceding a dividend record date. An enrollment form may also be obtained by contacting the Agent at 1-800-564-6253. If you are a beneficial holder, and you fill out and send the enrollment form to the Agent, you will NOT be enrolled in the Plan. Please see above instructions for beneficial holders to enroll in the Plan.

5. When will my dividends start reinvesting after I enroll in the Plan?

Eligible holders of common shares who return duly completed and signed Enrollment Forms that are received by the Agent no later than 4:00 p.m. (Toronto time) on the fifth business day immediately preceding a dividend record date will be eligible to reinvest the dividend associated with that record date. Once enrolled, participation in the Plan continues automatically unless participation is terminated in accordance with the Plan. If the Agent receives the completed Enrollment Form after 4:00 p.m. (Toronto time) on the fifth business day immediately preceding a dividend record date, the cash dividend in respect of that dividend record date will be paid to the shareholder in the usual manner and participation in the Plan will commence with the next dividend.

6. How are common shares purchased under the Plan?

The common shares purchased under the Plan will be purchased by the Agent, as plan agent on behalf of participants, directly from the Company as newly-issued shares from treasury.

7. Can participants purchase additional common shares under the Plan over and above those which their dividends will buy?

No. The Agent will only purchase common shares under the Plan using dividends paid on participants' common shares.

8. What price will be paid for the shares purchased under the Plan?

The subscription price of common shares purchased under the Plan will be the weighted average of the trading price for common shares on the stock exchange with the highest volume of common shares traded for the five trading days preceding the relevant dividend payment date as determined by the Company less a discount of 3%. If the trading price used is from the NYSE, the exchange rate from U.S. dollars to Canadian dollars to determine the Plan price will be the Bank of Canada noon rate of exchange on the dividend payment date.

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9. Do I still have to pay withholding tax on dividends that are reinvested?

Participation in the Plan generally does not change the taxable status of the dividends that are reinvested. Dividends that are subject to withholding tax when paid in cash will still be subject to the same withholding tax when reinvested and dividends that are taxable income to the shareholder will generally still be taxable when they are reinvested under the terms of the Plan. Please contact your tax advisor as individual tax circumstances differ.

10. How much does it cost to participate in the Plan?

There are no commissions, service charges or brokerage fees payable by participants with respect to share purchases under the Plan because the participant purchases new common shares directly from us. All administrative costs of the Plan, including the fees and expenses of the Agent, are borne by us.

11. Can I reinvest a portion of my monthly dividend?

No. Eligible holders of common shares who choose to participate in the Plan must reinvest the entire amount (less any applicable withholding taxes) of their monthly dividend.

12. Can a participant withdraw shares held in the Plan?

13. How do I terminate my participation in the Plan?

Participation in the Plan may be terminated by a Registered Participant who is enrolled in the Plan at any time by completing and signing the termination portion of the voucher located on the reverse of the Registered Participant's periodic statement of account and sending such completed and signed voucher to the Agent no later than 4:00 p.m. (Toronto time) on the fifth business day immediately preceding a dividend record date or by following the instructions on the Agent's Investor Centre web portal, at www.computershare.com/investorcentrecanada. The Agent will issue a common share certificate or direct registration system advice for the whole Plan shares and a cash payment for the fractional portion at the market price at the time of sale. A Beneficial Participant can terminate their participation in the Plan by giving notice to his, her or its financial institution or stock brokerage through which their common shares are held. Termination by a participant will not prevent such shareholder from participating in the Plan at a later date.

14. What kind of statements will be sent to participants in the Plan?

An account will be maintained by the Agent for each Registered Participant in the Plan. An unaudited quarterly statement of account will be mailed to each Registered Participant as soon as practicable following the last day of March, June, September and December, and the appropriate information for tax reporting purposes will be sent by the Agent to each Registered Participant on an annual basis. Beneficial Participants should consult their financial institution or stock brokerage in order to determine the type of reporting they will receive.

15. I am not a resident of Canada or the United States. Can I still participate?

No. The Plan is only open to holders of common shares who are residents of Canada or the United States.

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Description of the Plan

PURPOSE

The Plan enables eligible holders of our common shares to invest cash dividends, if, as and when declared and paid on our common shares, to acquire additional common shares. Common shares purchased under the Plan will be purchased directly from treasury by the Agent who acts on behalf of participants under the Plan. Proceeds from common shares purchased from treasury under the Plan will be used by the Company for general corporate purposes, which may include the repayment or refinancing of outstanding indebtedness.

ADVANTAGES

Under the Plan:

•: A participant may purchase additional common shares with the cash dividends (net of any applicable withholding taxes) paid on the common shares which are held by the participant or held in a participant's account maintained pursuant to the Plan.
•: The price at which common shares will be issued from treasury on reinvestment of cash dividends on common shares will be equal to the Average Market Price (as defined below), less a discount of 3%.
•: No commissions, service charges or brokerage fees are payable by participants in connection with the issuance of common shares from treasury to participants under the Plan.
•: Full investment of participants' funds is possible under the Plan because the Plan permits fractions of common shares as well as whole common shares to be purchased and held for participants.
•: Dividends in respect of common shares purchased under the Plan will be held by the Agent for the participants' accounts and automatically invested under the Plan in additional common shares of the Company.

ADMINISTRATION

Computershare Trust Company of Canada acts as the Agent for the participants under the Plan pursuant to an agreement which may be terminated by the Company or the Agent at any time upon 60 days prior written notice to the other party. On each dividend payment date, the Company shall pay to the Agent on behalf of the participants all cash dividends payable in respect of such participants' common shares (less any applicable withholding taxes). The Agent shall use such funds to purchase common shares for the participants. Common shares purchased under the Plan will be registered in the name of the Agent, as agent for participants in the Plan. Should Computershare Trust Company of Canada cease to act as Agent under the Plan, another agent will be designated by the Company, in its discretion.

The terms of the Plan are intended to comply with the requirements of the Tax Act (as defined below) and the administrative policies and assessing practices of the Canada Revenue Agency, and shall be interpreted and administered in accordance with all such requirements notwithstanding any other provision of this Plan to the contrary.

ELIGIBILITY

All holders of common shares who are Canadian or U.S. residents are eligible to participate in the Plan at any time by enrolling in the Plan as described below.

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Upon ceasing to be eligible to participate in the Plan, a participant shall forthwith notify the Agent in writing and terminate his, her or its participation in the Plan. The right to participate in the Plan may not be transferred or assigned by a participant.

ENROLLMENT

Any eligible registered shareholder may become a participant in the Plan (a "Registered Participant") at any time by completing an Enrollment Form online or by downloading and duly completing and signing an Enrollment Form at www.computershare.com/investorcentrecanada and returning it to the Agent no later than 4:00 p.m. (Toronto time) on the fifth business day immediately preceding a dividend record date.

A shareholder who is a beneficial and not an owner of record of common shares (e.g., whose shares are held by, and registered in the name of, a bank, trust company, investment dealer or other intermediary for the account of the participant) (a "Beneficial Participant") must make arrangements with the bank, trust company, investment dealer or other intermediary through which they hold their common shares to enroll as a participant in the Plan, as described above, or will be required to transfer such common shares into his, her or its own name or into a specific segregated registered account such as a numbered account with a bank, trust company, investment dealer or other intermediary in order for that person to become a Registered Participant.

Once a Registered Participant or Beneficial Participant has enrolled in the Plan, participation continues automatically unless terminated in accordance with the Plan.

An Enrollment Form may be accessed online as described above or may be obtained at any time upon written request addressed to the Agent.

If the Agent receives the completed Enrollment Form after 4:00 p.m. (Toronto time) on the fifth business day immediately preceding a dividend record date, the cash dividend in respect of that dividend record date will be paid to the shareholder in the usual manner and participation in the Plan will commence with the next dividend.

Once a participant is enrolled, the Company will forward to the Agent all of the participant's cash dividends on common shares (less any applicable withholding taxes) and direct the Agent to invest such amounts in common shares of the Company for the benefit of the participant. The Agent will apply such funds received under the Plan to the purchase of additional common shares under the Plan.

No interest will be paid to participants on any funds held for investment under the Plan.

PURCHASE AND VALUATION OF SHARES UNDER THE PLAN

The subscription price of common shares purchased from treasury under the Plan will be the weighted average of the trading price for common shares on the stock exchange with the highest volume of common shares traded for the five trading days preceding the relevant dividend payment date (the "Average Market Price") as determined by the Company, less a discount of 3%. If that stock exchange is the NYSE, the exchange rate from U.S. dollars to Canadian dollars shall be the Bank of Canada noon rate of exchange on the dividend payment date.

Each Registered Participant's account will be credited with that number of common shares purchased for the Registered Participant, including fractional common shares computed to six decimal places, which is equal to the amounts to be invested for each Registered Participant divided by the applicable purchase price. In the case of Beneficial Participants, this account will be maintained by CDS Clearing and Depository Services Inc. ("CDS") or the Beneficial Participant's financial institution or stock brokerage holding common shares as registered shareholder. Beneficial Participants should

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contact their financial institution or stock brokerage as to the manner in which fractional entitlements will be held.

Dividends paid on common shares held by the Agent for the account of a participant under the Plan will be automatically reinvested in common shares during the relevant month for such dividend payment.

COSTS

There are no commissions, service charges or brokerage fees payable by participants with respect to share purchases under the Plan because the participant purchases new common shares directly from the Company. All administrative costs of the Plan, including the fees and expenses of the Agent, are borne by the Company.

REPORTS TO PARTICIPANTS

An account will be maintained by the Agent for each Registered Participant in the Plan. An unaudited statement of account will be mailed to each Registered Participant quarterly as soon as practicable following the last day of each of March, June, September and December. These statements are a Registered Participant's continuing record of purchases and should be retained for income tax purposes. In addition, each Registered Participant will be sent annually by the Agent the appropriate information for tax reporting purposes. Registered Participants are responsible for calculating and monitoring their own adjusted cost base in common shares for income tax purposes, as certain averaging rules may apply and such calculations may depend on the cost of other common shares held by the participant. Beneficial Participants should consult their financial institution or stock brokerage in order to determine the type of reporting they will receive.

CERTIFICATES FOR COMMON SHARES

Common shares purchased under the Plan will be registered in the name of the Agent (or its nominee), as agent for participants in the Plan, and certificates for such common shares will not be issued to Registered Participants unless specifically requested.

A Registered Participant who is enrolled in the Plan may withdraw whole common shares under the Plan without terminating his, her or its participation in the Plan by duly completing the withdrawal portion of the voucher located on the reverse of the Registered Participant's periodic statement of account and sending such completed voucher to the Agent. Upon receipt of such duly completed voucher, the Agent will arrange to have a common share certificate or a Direct Registration System Advice ("DRS Advice") issued in the Registered Participant's name. Normally, a common share certificate or DRS Advice will be sent to a Registered Participant within two weeks of receipt by the Agent of a Registered Participant's duly completed voucher requesting withdrawal of whole common shares. Any remaining whole common shares and fractions of a common share will continue to be held for the Registered Participant's account under the Plan.

Each Registered Participant's account under the Plan is maintained in the name in which the Registered Participant entered the Plan. Consequently, certificates or a DRS Advice for whole common shares will be similarly registered when issued.

Beneficial Participants should consult their financial institution or stock brokerage in order to obtain certificates for common shares purchased on their behalf under the Plan.

Common shares held by the Agent for a participant under the Plan may not be pledged, sold or otherwise disposed of by the participant while so held. A participant who wishes to effect any such transaction must request that certificates or a DRS Advice for such shares be issued in the participant's name.

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TERMINATION OF PARTICIPATION

Participation in the Plan may be terminated by a Registered Participant who is enrolled in the Plan at any time by duly completing and signing the termination portion of the voucher located on the reverse of the Registered Participant's periodic statement of account and sending such completed and signed voucher to the Agent no later than 4:00 p.m. (Toronto time) on the fifth business day immediately preceding a dividend record date or by following the instructions at the Agent's Investor Centre web portal, at www.computershare.com/investorcentrecanada within such timeframe. A Beneficial Participant's participation in the Plan may be terminated by giving notice to his, her or its financial institution or stock brokerage through which its common shares are held.

If the completed voucher is received by 4:00 p.m. (Toronto time) at least five business days prior to a dividend record date, termination of the Registered Participant's participation in the Plan will be effective in respect of that dividend record date. Otherwise, the termination will be effective in respect of the next succeeding dividend record date. For greater certainty, termination by a Registered Participant will not prevent such shareholder from participating in the Plan at a later date. No certificate or DRS Advice requests will be processed between the dividend record date and the related dividend payment date.

When a Registered Participant terminates participation in the Plan, the Registered Participant will receive a certificate or DRS Advice for the whole common shares held for such Registered Participant's account and a cash payment for any fraction of a common share so held. Fractional common shares will be sold by the Agent on the TSX on a commingled basis, and the cash payment for a fractional common share interest will be calculated using the closing market price on the TSX or otherwise on the open market, as applicable, on the date of the sale of such common shares. Beneficial Participants should contact their financial institution or stock brokerage as to the manner in which the termination of their participation in the Plan will be handled, including with respect to fractional common share entitlements.

Participation in the Plan will be terminated automatically upon receipt by the Agent of a written notice of the death of a Registered Participant. A certificate for whole common shares or DRS Advice held for the deceased Registered Participant's account will be issued by the Agent in the name of the deceased Registered Participant or in the name of the estate of the deceased Registered Participant, as appropriate, and the Agent will send such certificate or DRS Advice and a cash payment for any fraction of a common share calculated in accordance with the previous paragraph to the legal representative of the deceased Registered Participant. No such termination will be made upon the death of a Beneficial Participant unless appropriate requests are made through such participant's financial institution or stock brokerage.

Participation in the Plan may be terminated, at the option of the Company, if the number of common shares purchased through the Plan by a participant over a period of 12 consecutive months does not exceed a certain minimum number of whole common shares determined by the Company, at its discretion, from time to time. Initially, this minimum number is set at one whole common share. Written notice of any such termination shall be given by the Company to the Agent no later than 4:00 p.m. (Toronto time) at least five business days prior to a dividend record date. In the event that participation is terminated by the Company for this reason, share certificates or a DRS Advice will be issued for all whole common shares held in the participant's account. Payment in respect of any fractional shares will be made to the participant in cash, calculated in same manner as set out for the treatment of fractional shares on terminating participation in the Plan as described above.

RIGHTS OFFERING

In the event the Company makes available to holders of common shares rights to subscribe for additional common shares or other securities, rights certificates will be issued by the Company to each

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Registered Participant (including CDS and financial institutions and stock brokerages holding common shares as registered holder on behalf of Beneficial Participants) in respect of whole common shares held for a Registered Participant's account under the Plan on the record date for such rights issue.

STOCK SPLITS AND STOCK DIVIDENDS

If common shares are distributed pursuant to a stock split or stock dividend on common shares, such common shares received by the Agent for participants under the Plan will be retained by the Agent and credited by the Agent proportionately to the accounts of the Registered Participants (including CDS and financial institutions and stock brokerages holding common shares as registered holder on behalf of Beneficial Participants) in the Plan.

SHAREHOLDER VOTING

Common shares held for a Registered Participant's account under the Plan on the record date for a vote of shareholders will be voted in accordance with the instructions of the Registered Participant given on a form to be furnished to the Registered Participant by the Agent. Common shares for which instructions are not received will not be voted. Beneficial Participants wishing to vote common shares held for their benefit under the Plan should consult their financial institution or stock brokerage.

RESPONSIBILITIES OF THE COMPANY AND THE AGENT

Neither the Company nor the Agent shall be liable for any act, or for any omission to act, in connection with the Plan including, without limitation, any claims for liability:

(a): arising out of failure to terminate a Registered Participant's account upon such Registered Participant's death prior to receipt of notice in writing of such death;
(b): with respect to the prices at which common shares are purchased for the participant's account and the times such purchases are made;
(c): arising out of any contravention by any participant of applicable securities laws with respect to his, her or its participation in the Plan or the acquisition or disposition of common shares;
(d): with respect to any actions taken as a result of inaccurate and incomplete information or instructions;
(e): arising in connection with income taxes (together with any applicable interest and/or penalties) payable by participants in connection with their participation in the Plan; and
(f): with respect to any decision to amend, suspend, terminate or replace the Plan in accordance with the terms hereof.

Registered Participants and Beneficial Participants should recognize that neither the Company nor the Agent can assure a profit or protect them against a loss of the common shares purchased under the Plan. No assurance is given that dividends will be declared in any particular amount or at all on the common shares.

AMENDMENT, SUSPENSION OR TERMINATION OF THE PLAN

The Company reserves the right to amend or suspend, in whole or in part, or terminate the Plan at any time subject, in the case of amendments, to any required stock exchange approval, but such action shall have no retroactive effect that would prejudice the interests of the participants. All Registered Participants (including CDS and financial institutions and stock brokerages holding common shares as registered holder on behalf of Beneficial Participants) will be sent written notice of any such amendment, suspension or termination.

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In the event of termination of the Plan by the Company, certificates, or a DRS Advice for whole common shares held for Registered Participants' accounts (including CDS and financial institutions and stock brokerages holding common shares as registered holder on behalf of Beneficial Participants) under the Plan and cash payments for any fraction of a common share will be remitted with due dispatch by the Agent to the Registered Participants (including CDS and financial institutions and stock brokerages holding common shares as registered holder on behalf of Beneficial Participants). Fractional common shares will be sold by the Agent on the TSX on a commingled basis, and the cash payment for a fractional common share interest will be calculated using the closing market price on the TSX or otherwise on the open market, as applicable, on the date of the sale of such common shares. In the event of suspension of the Plan by the Company, no investment will be made by the Agent on the dividend payment date immediately following the effective date of such suspension. Any dividends on common shares which are subject to the Plan and which are paid after the effective date of such suspension will be remitted in cash by the Agent to the Registered Participants (including CDS and financial institutions and stock brokerages holding common shares as registered holder on behalf of Beneficial Participants).

RULES AND REGULATIONS

The Company, in conjunction with the Agent, may from time to time adopt rules and regulations to facilitate the administration of the Plan. The Company also reserves the right to regulate and interpret the Plan as it deems necessary or desirable to ensure the efficient and equitable operation of the Plan.

COMPLIANCE WITH LAWS

The operation and implementation of the Plan is subject to compliance with all applicable legal requirements, including obtaining all appropriate regulatory approvals and exemptions from registration and prospectus requirements, and the requirements of any stock exchange on which the common shares are listed. The Company may limit the common shares issuable under the Plan in connection with any discretionary exemptive relief relating to the Plan granted by any securities regulatory authority.

GOVERNING LAW

The Plan shall be construed in accordance with the laws of the Province of British Columbia and the federal laws of Canada applicable therein.

RISK OF MARKET PRICE FLUCTUATIONS

Participants should recognize that common shares acquired under the Plan are no different from an investment in common shares directly held. Accordingly, neither the Company nor the Agent can assure a profit or protect participants against a loss on the common shares purchased under the Plan.

CURRENCY

All monetary amounts identified in the Plan are stated in Canadian dollars, unless otherwise expressly stated.

NOTICES

All notices required to be given under the Plan shall be mailed to each Registered Participant (including CDS and financial institutions and stock brokerages holding common shares as registered holder on behalf of Beneficial Participants) at the address shown on the records of the Agent or at a more recent address as furnished by the Registered Participant.

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Notices to the Agent shall be addressed as follows:

Computershare Trust Company of Canada
100 University Avenue, 9th Floor
North Tower
Toronto Ontario
M5J 2Y1

Attention: Dividend Reinvestment Department

Or the National Customer Contact Centre at 1-800-564-6253

Or by visiting www.computershare.com/service

Notices to the Company shall be addressed as follows:

Atlantic Power Corporation
One Federal Street, 30th Floor
Boston, MA 02110

Attention: Corporate Secretary
Fax No: (617)977-2410

EFFECTIVE DATE OF THE PLAN

The effective date of the Plan is August 8, 2012.

Certain Canadian Federal Income Tax Considerations

The following is a summary of the principal Canadian federal income tax considerations generally applicable to a participant that, at all relevant times, for purposes of the application of the Income Tax Act (Canada) (the "Tax Act") and the Income Tax Regulations (the "Regulations"), deals at arm's length with and is not affiliated with the Company and holds shares acquired under the Plan as capital property (a "Typical Participant"). This summary is not exhaustive of all possible Canadian federal income tax considerations, and does not take into account Canadian provincial or territorial income tax laws, or foreign tax considerations.

This summary does not apply to a participant: (i) that is subject to the "mark-to-market" rules under the Tax Act applicable to certain "financial institutions"; (ii) that is a "specified financial institution"; (iii) an interest in which is a "tax shelter investment"; or (iv) to which the "functional currency" reporting rules apply (all as defined in the Tax Act).

This summary is based upon the provisions of the Tax Act and the Regulations in force as of the date hereof, all specific proposals to amend the Tax Act and the Regulations that have been publicly announced by the Minister of Finance (Canada) prior to the date hereof and the current published administrative policies and assessing practices of the Canada Revenue Agency as of the date hereof. This summary does not otherwise take into account or anticipate any changes in law or administrative practices, whether by legislative, governmental or judicial account.

This summary is of a general nature only and is not, and is not intended to be, legal or tax advice to any particular participant under the Plan. This summary is not exhaustive of all Canadian federal income tax considerations. Accordingly, prospective participants should consult their own tax advisers having regard to their own particular circumstances.

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Canadian Residents

This portion of the summary is generally applicable to a Typical Participant that, at all relevant times, for purposes of the application of the Tax Act, is, or is deemed to be resident in Canada (a "Canadian Participant").

All cash dividends paid on common shares that are reinvested on behalf of a Canadian Participant will generally be subject to the tax treatment normally applicable to taxable dividends from taxable Canadian corporations. For example, in the case of a Canadian Participant who is an individual, such dividends will be subject to the normal gross-up and credit rules or, in the case of a Canadian Participant that is a private corporation or one of certain other corporations, a refundable tax will apply to the amount of the dividend. Other taxes could apply depending on the circumstances of the Canadian Participant.

The right granted under the terms of the Plan to reinvest cash dividends paid on common shares in common shares newly-issued from treasury at the Average Market Price, less a discount of 3% of the Average Market Price, and the exercise of such right, should not give rise to a taxable benefit under the Tax Act.

A Canadian Participant will not realize any taxable income when the participant receives certificates for whole common shares credited to the Participant's account, either upon the Participant's request, upon termination of participation or upon termination of the Plan.

The cost to a Canadian Participant of common shares acquired under the Plan will be the price paid for the shares by the Canadian Participant. For the purpose of computing the adjusted cost base of such shares to the Canadian Participant, the cost of the shares will be averaged with the adjusted cost base of all common shares of the Company held by the Canadian Participant as capital property.

A Canadian Participant may realize a capital gain or loss on the disposition of shares acquired through the Plan, including on the disposition of a fraction of a common share in consideration for cash upon termination of participation in the Plan or upon termination of the Plan.

U.S. Residents

This portion of the summary is generally applicable to a Typical Participant that, at all relevant times: (i) is not resident in Canada for purposes of the application of the Tax Act, , (ii) is a resident of the United States for the purposes of the Canada-U.S. Income Tax Convention (1980), as amended (the "Treaty") and (iii) does not carry on business in Canada (a "U.S. Participant"). Special rules, which are not discussed in this summary, may apply to a U.S. Participant that is an insurer that carries on an insurance business in Canada and elsewhere.

All cash dividends paid on common shares that are reinvested on behalf of a U.S. Participant will generally be subject to the tax treatment normally applicable to taxable dividends from taxable Canadian corporations. Dividends which a U.S. Participant designates for investment under the Plan will be subject to Canadian withholding tax at the rate of 25%, subject to any reduction in the rate of withholding to which the U.S. Participant is entitled under the Treaty. Where a U.S. Participant is fully entitled to benefits under the Treaty and is the beneficial owner of the dividends, the applicable rate of Canadian withholding tax is generally reduced to 15%. The amount of dividends to be invested under the Plan will be reduced by the amount of tax withheld.

The disposition of a fraction of a common share in consideration for cash (either upon the U.S. Participant's request, upon termination of participation or upon termination of the Plan) may give rise to a deemed dividend subject to withholding tax.

Gains on the disposition of common shares by a U.S. Participant (including upon the disposition of a fractional common share) are generally not subject to Canadian income tax unless such shares are or

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are deemed to be "taxable Canadian property" within the meaning of the Tax Act and the U.S. Participant is not entitled to relief under any applicable income tax convention. If the common shares are listed on a "designated stock exchange" (which includes the TSX and the NYSE) at a particular time, such shares will not constitute taxable Canadian property to a U.S. Participant at such time provided that at any time during the sixty-month period that ends at that time, either: (a) the U.S. Participant, persons with which the U.S. Participant does not deal at arm's length, or the U.S. Participant together with all such persons, have not owned 25% or more of any class or series of shares of the capital stock of the Company; or (b) such common shares did not derive, directly or indirectly, more than 50% of their fair market value from one or any combination of (i) real or immovable property situated in Canada, (ii) "Canadian resource properties" (as defined in the Tax Act), (iii) "timber resource properties" (as defined in the Tax Act), and (iv) options or interests in respect of property described in (i), (ii) and (iii).

Certain United States Tax Considerations for United States Residents

The following is a general summary of the principal U.S. federal income tax consequences of the ownership of common shares and participation in the Plan as of the date hereof. The summary is applicable to U.S. holders (as defined below) who are residents of the U.S. for purposes of the current Canada-United States Income Tax Convention (1980), as amended. Except where noted, it deals only with common shares held as capital assets and it does not deal with all tax aspects that might be relevant to a prospective stockholder in light of its personal circumstances, nor does it deal with particular types of stockholders that are subject to special treatment under the federal income tax laws, such as (i) insurance companies; (ii) tax-exempt organizations; (iii) financial institutions or broker-dealers; (iv) non-U.S. individuals and foreign corporations; (v) U.S. expatriates; (vi) persons who mark-to-market our common shares; (vii) subchapter S corporations; (viii) U.S. holders whose functional currency is not the U.S. dollar; (ix) regulated investment companies; (x) holders who receive common shares through the exercise of employee stock options or otherwise as compensation; (xi) persons holding shares of common shares as part of a "straddle," "hedge," "conversion transaction," "synthetic security" or other integrated investment; (xii) persons subject to the alternative minimum tax provisions of the Code; (xiii) persons holding common shares through a partnership or similar pass-through entity; and (xiv) persons holding a 10% or more (by vote or value) beneficial interest in the Company. Furthermore, the discussion below is based upon the provisions of the Internal Revenue Code of 1986, as amended (the "Code"), and regulations, rulings and judicial decisions thereunder as of the date hereof, and such authorities may be repealed, revoked or modified so as to result in U.S. federal income tax consequences different from those discussed below. This summary does not address all possible tax considerations that may be material to an investor and does not constitute legal or tax advice. Persons considering the purchase, ownership or disposition of common shares should consult their own tax advisors concerning the U.S. federal income tax consequences in light of their particular situations as well as any consequences arising under the laws of any other taxing jurisdiction, including state, local and foreign jurisdictions.

As used herein, the term "U.S. holder" means a beneficial holder of a common share that is (i) a citizen or resident of the U.S., (ii) a corporation or partnership created or organized in or under the laws of the U.S. or any political subdivision thereof, (iii) an estate the income of which is subject to U.S. federal income taxation regardless of its source or (iv) a trust if it (x) is subject to the supervision of a court within the U.S. and one or more U.S. persons have the authority to control all substantial decisions of the trust, or (y) that has a valid election in effect under applicable U.S. Treasury regulations to be treated as a U.S. person.

If a partnership, including any entity treated as a partnership for U.S. federal income tax purposes, holds common shares, the U.S. federal income tax treatment of a partner in the partnership will generally depend on the status of the partner and the activities of the partnership. If one is a partner in

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a partnership holding common shares, such partner is urged to consult one's tax advisor regarding the consequences of the ownership and disposition of common shares by the partnership.

Distributions Generally

A U.S. holder who participates in the Plan generally will be treated for U.S. federal income tax purposes as having received a distribution from the Company with respect to its common shares equal to the sum of (a) the fair market value of the common shares credited to the shareholder's Plan account, (b) any cash distributions actually received by the shareholder with respect to common shares not included in the Plan, (c) any applicable sales or brokerage fees the Company pays on the U.S. holder's behalf, and (d) any fees or tax withholdings, including Canadian withholding taxes, subtracted from a distribution prior to purchase of common shares. The total amount of cash dividends and other distributions will be reported to the U.S. holder and to the Internal Revenue Service on the appropriate tax form after the end of each year. U.S. holders should consult their tax advisors regarding the deductibility of any fees subtracted from cash distributions prior to reinvestment of such distributions in common shares. The amount of the distribution deemed received may exceed the amount of the cash dividend that was reinvested if the Company offers a discount on the purchase price of the common shares.

Distributions to U.S. holders, including any deemed dividend resulting from a discount in the purchase price as discussed below, will constitute dividends to the extent of the Company's current or accumulated earnings and profits as determined for U.S. federal income tax purposes. The Code requires this treatment even though a U.S. holder will never actually receive the reinvested dividends in cash because its dividends are used instead to purchase common shares.

If a U.S. holder so elects with respect to all foreign taxes, it will be entitled to a credit against its U.S. federal income tax liability for the Canadian withholding tax imposed on those dividends. The amount of the credit will be subject to limitations contained in the foreign tax credit provisions of the Code. A U.S. holder that finds that, because of such limitations, it is more advantageous in its particular case to claim Canadian withholding tax as a deduction rather than as a credit may do so, but only for a year for which the U.S. holder elects to do so with respect to all foreign taxes.

To the extent that the Company makes a distribution in excess of its current and accumulated earnings and profits, the distribution will be treated first as a tax-free return of capital, reducing the tax basis in the U.S. holder's shares, and the amount of each distribution in excess of a U.S. holder's tax basis in its shares will be taxable as gain realized from the sale of its common shares.

Certain costs of administering the Plan will be paid by the Company. Consistent with the conclusion reached by the Internal Revenue Service in a private letter ruling, the Company intends to take the position that these administrative costs do not constitute a distribution which is either taxable to a U.S. holders or which would reduce a U.S. holder's basis in its common shares. However, because the private letter ruling was not issued to the Company, the Company has no legal right to rely on its conclusions. Thus, it is possible that the Internal Revenue Service might view a U.S. holder's share of the costs as constituting a taxable distribution to such U.S. holder, and/or a distribution which reduces the basis of such U.S. holder's common shares. For this or other reasons, the Company may in the future take a different position with respect to these costs.

Subject to the following discussion, the tax basis for the common shares acquired by reinvesting cash distributions through the Plan generally will equal the amount treated as a distribution to a U.S. holder for federal income tax purposes. Absent an election to the contrary from a U.S. holder, the Agent intends to use the "first in first out" (or "FIFO") basis method (as defined in applicable Treasury Regulations) for computing the tax basis of the Common Shares acquired by or for a U.S holder under the Plan. The FIFO method will apply to common shares acquired by or for a U.S. holder under the Plan, except to the extent a U.S. holder provides notice to the Agent that such U.S.

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holder elects to use another permitted method of computing the tax basis of such U.S. holder's shares under the Plan. A U.S. holder should consult one's tax advisor regarding whether the "average basis method" is available for some or all of the common shares acquired in connection with the Plan and which tax basis methods and elections are appropriate for such U.S. holder. The holding period for common shares purchased under the Plan (including a fractional share) generally will begin on the day following the date of acquisition. We urge each U.S. holder to save account statements in order to calculate one's tax basis per each common share.

The amount of any dividend paid in Canadian dollars will equal the U.S. dollar value of the Canadian dollars received calculated by reference to the exchange rate in effect on the date the dividend is received by the U.S. holder regardless of whether the Canadian dollars are converted into U.S. dollars. If the Canadian dollars received as a dividend are not converted into U.S. dollars on the date of receipt, a U.S. holder will have a basis in the Canadian dollars equal to the U.S. dollar value on the date of receipt. Any gain or loss realized on a subsequent conversion or the disposition of the Canadian dollars will be treated as ordinary income or loss.

Certain Dispositions of Shares of the Common Shares

U.S. holders will not recognize gain or loss for U.S. federal income tax purposes merely upon withdrawal of common shares previously credited to a U.S. holder's Plan account. However, a U.S. holder will realize a gain or loss when common shares are sold or exchanged, whether pursuant to the U.S. holder's request upon termination of participation in the Plan or by the U.S. holder after receipt of common shares from the Plan, and, in the case of any fraction of a common share, when the Participant receives a cash adjustment for a fraction of a common share. The amount of such gain or loss will be the difference between the amount which the U.S. holder receives for the common shares or fraction of a common share and the tax basis therefor. The gain or loss will be a capital gain or loss. Losses recognized by a U.S. holder upon the disposition of shares of the common shares will be considered capital losses, and are generally available only to offset capital gain income of the U.S. holder but not ordinary income (except in the case of individuals, who may offset up to $3,000 of ordinary income each year). All or a portion of any loss realized upon a taxable disposition of common shares may be disallowed if the taxpayer purchases other common shares within 30 days before or after the disposition.

Information Reporting Requirements and Backup Withholding for U.S. holders

The Company may be required to report to U.S. holders and to the Internal Revenue Service the amount of distributions made or deemed made during each calendar year and the amount of tax withheld, if any. Under some circumstances, U.S. holders may be subject to backup withholding on payments made with respect to, or cash proceeds of a sale or exchange of, common shares. Backup withholding will apply only if the holder (i) fails to furnish its taxpayer identification number (which, for an individual, would be his or her Social Security number); (ii) furnishes an incorrect taxpayer identification number; (iii) is notified by the Internal Revenue Service that the U.S. holder has failed properly to report payments of interest or distributions and is subject to backup withholding; or (iv) under some circumstances, fails to certify, under penalties of perjury, that it has furnished a correct taxpayer identification number and has not been notified by the Internal Revenue Service that the U.S. holder is subject to backup withholding for failure to report interest and distribution payments or has been notified by the Internal Revenue Service that the U.S. holder is no longer subject to backup withholding for failure to report those payments.

Backup withholding will not apply with respect to payments made to some U.S. holders, such as corporations in certain circumstances and tax-exempt organizations. Backup withholding is not an additional tax. Rather, the amount of any backup withholding with respect to a payment to a U.S. holder will be allowed as a credit against the U.S. holder's United States federal income tax liability

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and may entitle the U.S. holder to a refund, provided that the required information is furnished to the Internal Revenue Service. U.S. holders should consult their tax advisors regarding their qualification for exemption from backup withholding and the procedure for obtaining an exemption.

Medicare Tax on Unearned Income

For taxable years beginning after December 31, 2012, certain U.S. holders that are individuals, estates or trusts will be required to pay an additional 3.8% tax (the "Medicare Tax") on, among other things, certain dividends on and capital gains from the sale or other disposition of stock. U.S. holders that are individuals, estates or trusts should consult their tax advisors regarding the effect, if any, of the Medicare Tax on their ownership and disposition of the common shares.

Tax consequences will vary depending on each U.S. holder's specific circumstances. Each U.S. holder should discuss specific tax questions regarding participation in the Plan with one's own tax advisor.

Plan of Distribution

We will sell directly to you, through the Agent, the common shares acquired under the Plan. The common shares may be resold in market transactions on any national securities exchange on which the common shares trade or in privately negotiated transactions. Our common shares trade on the TSX under the symbol "ATP" and on the NYSE under the symbol "AT."

We may sell our common shares under the Plan to persons, including brokers or dealers and other financial intermediaries, that, in connection with any resales of those shares, may be deemed to be underwriters within the meaning of the Securities Act of 1933. We have no arrangements or understandings, formal or informal, with any person relating to the sale of shares of our common shares to be received under the Plan. We will not extend to any such person any rights or privileges other than those to which it would be entitled as a participant under the Plan, nor will we enter into any agreement with any such person regarding such person's purchase of such shares or any resale of distribution thereof.

Subject to the availability of common shares registered for issuance under the Plan, there is no total maximum number of common shares that can be issued to any particular shareholder pursuant to the reinvestment of dividends. For additional information, see "Description of the Plan"

Our common shares may not be available under the Plan in all states or other jurisdictions. We are not making an offer to sell our common shares in any state or other jurisdiction where the offer or sale is not permitted.

Legal Matters

Certain legal matters relating to the issue and sale of the common shares offered hereby will be passed upon for us by Goodmans.

Experts

The consolidated financial statements and financial statement schedule of Atlantic Power Corporation as of December 31, 2011 and 2010 and for each of the years in the three-year period ended December 31, 2011 appearing in Atlantic Power's Annual Report on Form 10-K for the year ended December 31, 2011, as amended (including the schedule appearing therein), have been so incorporated by reference herein in reliance upon the reports of the United States and Canadian firms of KPMG LLP, independent registered public accounting firms, incorporated by reference herein, and upon the authority of said firms as experts in accounting and auditing.

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The financial statements of Chambers Cogeneration Limited Partnership as of December 31, 2010 and for the year then ended incorporated in this registration statement by reference to Atlantic Power's Annual Report on Form 10-K for the year ended December 31, 2011, as amended, have been so incorporated in reliance on the report (which contains an explanatory paragraph relating to the Chambers Cogeneration Limited Partnership restatement of its financial statements as described in the Restatement of Previously Issued Financial Statements section of Note 2 to the financial statements) of PricewaterhouseCoopers LLP, independent auditors, given on the authority of said firm as experts in auditing and accounting.

The consolidated financial statements of Capital Power Income L.P. as of December 31, 2010 and 2009 and for each of the years in the three year period ended December 31, 2010, incorporated by reference into this registration statement by reference to Atlantic Power's Current Report on Form 8-K/A filed with the SEC on December 20, 2011, have been so incorporated by reference herein in reliance on the report of the Canadian firm of KPMG LLP, an independent registered public accounting firm, and upon the authority of said firm as experts in auditing and accounting.

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Table of Contents

PROSPECTUS

Common Shares
Debt Securities

We may offer from time to time our common shares and debt securities. We will provide specific terms of the securities which we may offer in supplements to this prospectus. You should read this prospectus and any prospectus supplement carefully before you invest. Securities may be sold for U.S. dollars or Canadian dollars.

Our common shares trade on the Toronto Stock Exchange (the "TSX") under the symbol "ATP" and on the New York Stock Exchange (the "NYSE") under the symbol "AT." The applicable prospectus supplement will contain information, where applicable, regarding the listing of the securities covered by such prospectus supplement or term sheet.

The securities may be offered directly by us or by any selling security holder, through agents designated from time to time by us or to or through underwriters or dealers. If any agents, dealers or underwriters are involved in the sale of any of the securities, their names and any applicable purchase price, fee, commission or discount arrangement between or among them will be set forth, or will be calculable from the information set forth, in the applicable prospectus supplement. See the sections entitled "About This Prospectus" and "Plan of Distribution" for more information.

Investing in our securities involves risks. See "Risk Factors" on page 7 before you make your investment decision.

The date of this prospectus is August 8, 2012.

Table of Contents

TABLE OF CONTENTS

		Page

About this Prospectus			4
Where You Can Find More Information			4
Our Company			5
Cautionary Note Regarding Forward-Looking Statements			6
Risk Factors			7
Use of Proceeds			7
Ratio of Earnings to Fixed Charges			8
Description of Common Shares			8
Description of Debt Securities			10
Plan of Distribution			26
Legal Matters			26
Experts			26

You should rely only on the information provided or incorporated by reference in this prospectus or any applicable prospectus supplement or any applicable free writing prospectus or, for prospective purchasers in Canada, the Canadian prospectus relating to this offering. If anyone provides you with different or additional information, you should not rely on it. We have not authorized anyone to provide you with different, inconsistent or additional information. We are not making an offer to sell these securities in any jurisdiction where the offer or sale of these securities is not permitted. You should not assume that the information appearing in this prospectus, any applicable prospectus supplement, any free writing prospectus or the documents incorporated by reference herein or therein is accurate as of any date other than their respective dates. Our business, financial condition, results of operations and prospects may have changed since those dates.

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About this Prospectus

This prospectus is part of an automatic shelf registration statement that we have filed with the Securities and Exchange Commission (the "SEC") as a "well-known seasoned issuer" as defined in Rule 405 under the Securities Act of 1933, as amended (the "Securities Act"), using a "shelf" registration process. Under this process, we may sell any combination of the securities described in this prospectus in one or more offerings. This prospectus provides you with a general description of the securities we may offer.

Each time we offer to sell securities, we will provide a supplement to this prospectus or a term sheet that will contain specific information about the terms of that offering. The prospectus supplement or a term sheet will describe the specific terms of that offering. The prospectus supplement or term sheet may also add to, update or change the information contained in this prospectus. Please carefully read this prospectus, the prospectus supplement and any term sheet together with the information contained in the documents we refer to under the heading "Where You Can Find More Information".

As used in this prospectus, the terms "Atlantic Power," the "Company," "we," "our" and "us" refer to Atlantic Power Corporation, together with those entities owned or controlled by Atlantic Power Corporation, unless the context indicates otherwise. Unless otherwise noted, all references to "C$," "Cdn$" and "Canadian dollars" are to the lawful currency of Canada and all references to "$," "US$" and "U.S. dollars" are to the lawful currency of the United States. This prospectus includes our trademarks and other trade names identified herein. All other trademarks and trade names appearing in this prospectus are the property of their respective holders.

Where You Can Find More Information

We file annual, quarterly and current reports, proxy statements and other information with the SEC. You may read and copy any document we file at the SEC's Public Reference Room at 100 F Street, N.E., Washington, D.C. 20549. You may call the SEC at 1-800-SEC-0330 for further information on the operation of the Public Reference Room. Our SEC filings are also available to the public from the SEC's website at http://www.sec.gov and on our website at http://www.atlanticpower.com. We have included the SEC's web address and our web address as inactive textual references only. Our website is not incorporated into, and does not constitute a part of, this prospectus or any other report or documents we file with or furnish to the SEC.

The SEC allows us to incorporate by reference the information we file with it, which means that we can disclose important information to you by referring you to these documents. The information incorporated by reference is an important part of this prospectus, and information that we file later with the SEC will automatically update and supersede the information already incorporated by reference. Atlantic Power's SEC file number is 001-34691. We are incorporating by reference the documents listed below, which were previously filed by us with the SEC:

•: our Annual Report on Form 10-K for the year ended December 31, 2011, filed with the SEC on February 29, 2012, as amended on April 2, 2012;
•: our Quarterly Report on Form 10-Q for the quarter ended March 31, 2012, filed with the SEC on May 7, 2012;
•: our Quarterly Report on Form 10-Q for the quarter ended June 30, 2012, filed with the SEC on August 8, 2012;
•: our annual Proxy Statement on Schedule 14A relating to our annual meeting of shareholders, filed with the SEC on April 30, 2012;

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•: our Current Reports on Form 8-K filed with the SEC on February 3, 2012, March 2, 2012, April 5, 2012, June 25, 2012, July 6, 2012 and July 16, 2012, except, in any such cases, the portions furnished and not filed pursuant to Item 7.01 or otherwise;
•: the audited consolidated financial statements of Capital Power Income L.P. and its subsidiaries as of December 31, 2010 and 2009 and for each of the three years ended December 31, 2010, 2009 and 2008, and the notes related thereto, filed as Exhibit 99.1 to our Current Report on Form 8-K/A, filed with the SEC on December 20, 2011;
•: the unaudited condensed interim consolidated financial statements of Capital Power Income L.P. and its subsidiaries as of and for the three and nine months ended September 30, 2011 and 2010 and the notes related thereto, filed as Exhibit 99.2 to our Current Report on Form 8-K/A, filed with the SEC on December 20, 2011;
•: the unaudited pro forma condensed combined consolidated statement of operations of the Company and Atlantic Power Limited Partnership for the year ended December 31, 2011 and the notes related thereto, included under the heading "Unaudited Pro Forma Condensed Consolidated Statement of Operations" in our prospectus filed with the SEC pursuant to Rule 424(b) on July 3, 2012;
•: the description of the Company's common shares contained in the Company's Registration Statement on Form 10, filed with the SEC on July 21, 2010; and
•: all documents filed by us with the SEC pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act after the date of this prospectus and prior to the termination of this offering, except as to any portion of any future report or document that is not deemed filed under such provisions.

You may request a copy of these filings, and any exhibits we have specifically incorporated by reference as an exhibit in this prospectus, at no cost by writing or telephoning us at the following: Atlantic Power Corporation, One Federal Street, Floor 30, Boston, Massachusetts 02110. Our telephone number is (617) 977-2400.

Our Company

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Our registered office is located at 355 Burrard Street, Suite 1900, Vancouver, British Columbia, Canada V6C 2G8 and our headquarters is located at One Federal Street, Floor 30, Boston, Massachusetts 02110 USA. Our telephone number in Boston is (617) 977-2400 and the address of our website is www.atlanticpower.com. We make available, free of charge, on our website our Annual Report on Form 10-K, Quarterly Reports on Form 10-Q, Current Reports on Form 8-K and amendments to those reports filed or furnished pursuant to Section 13(a) or 15(d) of the Exchange Act as soon as reasonably practicable after we electronically file such material with, or furnish it to, the SEC. Additionally, we make available on our website, our Canadian securities filings. Other than specific documents incorporated by reference, information on our web site is not incorporated into this prospectus or our other securities filings and does not form a part of this prospectus.

Cautionary Note Regarding Forward-Looking Statements

This prospectus, the prospectus supplements, the documents incorporated or deemed to be incorporated by reference in this prospectus and other written or oral statements made from time to time by the Company may contain forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995 with respect to the financial condition, results of operations, business strategies, operating efficiencies, synergies, revenue enhancements, competitive positions, plans and objectives of management and growth opportunities of Atlantic Power Corporation, and with respect to the markets for Atlantic Power common shares and other matters. Statements in this prospectus and the documents incorporated by reference herein that are not historical facts are hereby identified as forward-looking statements for the purpose of the safe harbor provided by Section 27A of the Securities Act and Section 21E of the Exchange Act and forward-looking information within the

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meaning defined under applicable Canadian securities legislation (collectively, "forward-looking statements").

•: the amount of distributions expected to be received from our projects;
•: the ability of the Company to generate sufficient amounts of cash and cash equivalents to maintain our operations and meet obligations as they become due;
•: the expected use of proceeds from offerings of our securities;
•: the impact of legislative, regulatory, competitive and technological changes;
•: expectations regarding completion of construction of certain projects; and
•: other risk factors relating to us and the power industry, as detailed from time to time in our filings with the SEC and the Canadian Securities Administrators.

You are cautioned that any forward-looking statement speaks only as of the date of this prospectus or, if such statement is included in a document incorporated by reference into this prospectus, as of the date of such other document. We undertake no obligation to update or revise any forward-looking statement, whether as a result of new information, future events or otherwise, except as may be required by applicable law.

Risk Factors

Investing in our securities involves risks. Before purchasing the securities offered by this prospectus you should carefully consider the risks, uncertainties and additional information (i) set forth in our most recent Annual Report on Form 10-K, as amended, any subsequent Quarterly Reports on Form 10-Q and SEC reports on Form 8-K, which are incorporated, or deemed to be incorporated, by reference into this prospectus, and in the other documents incorporated by reference in this prospectus that we file with the SEC after the date of this prospectus and which are deemed incorporated by reference in this prospectus, and (ii) contained in any applicable prospectus supplement. For a description of these reports and documents, and information about where you can find them, see "Where You Can Find More Information." The risks and uncertainties in the documents incorporated by reference in this prospectus are those that we currently believe may materially affect our company. Additional risks not presently known or that are currently deemed immaterial could also materially and adversely affect our financial condition, results of operations, business and prospects.

Use of Proceeds

Unless otherwise set forth in a prospectus supplement, we intend to use the net proceeds of any offering of common shares and debt securities offered by this prospectus for working capital and other general corporate purposes, which may include the repayment or refinancing of outstanding indebtedness and the financing of future acquisitions. We will have significant discretion in the use of

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any net proceeds. The net proceeds may be invested temporarily in interest-bearing accounts and short-term interest-bearing securities until they are used for their stated purpose. We may provide additional information on the use of the net proceeds from the sale of the offered securities in an applicable prospectus supplement relating to the offered securities.

We will not receive any proceeds in the event that securities offered and sold hereunder are those being re-sold into the public markets by an existing securityholder.

Ratio of Earnings to Fixed Charges

The following table sets forth our ratios of earnings to fixed charges for the periods indicated calculated on the basis of the U.S. GAAP financial statements incorporated by reference in this prospectus. For this purpose, "earnings" consists of earnings from continuing operations and distributed income of equity investees, excluding income taxes, non-controlling interests share in earnings and fixed charges, other than capitalized interest, and "fixed charges" consists of project-level interest expense and corporate level interest expense.

	Year Ended December 31,										Six Months Ended June 30, 2012

	2011		2010		2009		2008		2007		Six Months Ended June 30, 2012
Ratio of Earnings to Fixed Charges		(1)		2.08		(1)		2.24		1.58		(1)

(1): For purposes of computing this ratio of earnings to fixed charges, fixed charges consist of project-level interest expense and corporate level interest expense. Earnings consist of earnings from continuing operations and distributed income of equity investees, excluding income taxes, non-controlling interests share in earnings and fixed charges, other than capitalized interest. Earnings were insufficient to cover fixed charges as the loss before taxes was $43.9 million and $54.2 million, for the years ended December 31, 2011 and 2009, respectively, and $63.1 million for the six months ended June 30, 2012.

Description of Common Shares

The following summary description sets forth some of the general terms and provisions of our common shares. Because this is a summary description, it does not contain all of the information that may be important to you. For a more detailed description of our common shares, you should refer to the provisions of our Articles of Continuance, which we refer to as our "Articles."

Common shares

Our Articles authorize an unlimited number of common shares. At the close of business on August 3, 2012, 119,248,868 of our common shares were issued and outstanding.

Our common shares are listed on the TSX under the symbol "ATP" and on the NYSE under the symbol "AT." Holders of our common shares are entitled to receive dividends as and when declared by our board of directors and are entitled to one vote per common share on a vote by poll, or one vote per person present who is a shareholder or a proxy holder for a vote by show of hands, in each case with respect to all matters to be voted on at meetings of shareholders. We are limited in our ability to pay dividends on our common shares by restrictions under the Business Corporations Act (British Columbia), which we refer to as the "BC Act," relating to our solvency before and after the payment of a dividend. Holders of our common shares have no statutory preemptive, conversion or redemption rights and are not subject to further assessment by us.

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Upon our voluntary or involuntary liquidation, dissolution or winding up, the holders of common shares are entitled to share ratably in the remaining assets available for distribution, after payment of liabilities.

Pursuant to our Articles and the provisions of the BC Act, certain actions that may be proposed by us require the approval of our shareholders. We may, by special resolution and subject to our Articles, increase our authorized capital by such means as creating shares with or without par value or increasing the number of shares with or without par value. We may, by special resolution and subject to the BC Act, alter our Articles to subdivide, consolidate, change from shares with par value to shares without par value or from shares without par value to shares with par value or change the designation of all or any of our shares. We may also, by special resolution and subject to the BC Act, alter our Articles to create, define, attach, vary, or abrogate special rights or restrictions to any shares. Under the BC Act and our Articles, a special resolution is a resolution passed at a duly-convened meeting of shareholders by not less than two-thirds of the votes cast in person or by proxy at the meeting, or a written resolution consented to by all shareholders who would have been entitled to vote at the meeting of shareholders.

Certain provisions of our Articles and the BC Act

We are governed by the BC Act. Our Articles contain provisions that could have the effect of delaying, deferring or discouraging another party from acquiring control of our company by means of a tender offer, a proxy contest or otherwise.

Advance notice procedures

Under the BC Act, shareholders may make proposals for matters to be considered at the annual general meeting of shareholders. Such proposals must be sent to us in advance of any proposed meeting by delivering a timely written notice in proper form to our registered office. The notice must include information on the business the shareholder intends to bring before the meeting. These provisions could have the effect of delaying until the next shareholder meeting shareholder actions that are favored by the holders of a majority of our outstanding voting securities. Our Articles establish an advance notice procedure for "special business" and shareholder proposals to be brought before a meeting of shareholders. For special business, advance notice describing the special business to be discussed at the meeting must be provided and that notice must include any documents to be approved or ratified as an addendum or state that such document will be available for inspection at our records office or other reasonably accessible location. Shareholders at an annual meeting may not consider proposals or nominations that are not specified in the notice of meeting or brought before the meeting by or at the direction of the board of directors or by a shareholder of record on the record date for the meeting or a proxyholder who is entitled to vote at the meeting.

Shareholder requisitioned meeting

Under the BC Act, shareholders holding in the aggregate ¹/20 of our outstanding common shares may request the directors to call a general meeting of shareholders to deal with matters that may be dealt with at a general meeting, including election of directors. If the directors do not call the meeting within the timeframes specified in the BC Act, the shareholder can call the meeting and we must reimburse the costs.

Removal of directors and increasing board size

Under our Articles, directors may be removed by shareholders by passing an ordinary resolution of a simple majority of shareholders with the right to vote on such resolution. Further, under our Articles

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and subject to the BC Act, the directors may appoint additional directors up to one-third of the directors elected by the shareholders.

Canadian securities laws

We are a reporting issuer in each of the provinces and territories of Canada and therefore subject to the securities laws in each such province and territory. Canadian securities laws require reporting of share purchases and sales by shareholders acquiring beneficial ownership of, or the power to exercise control or direction over, 10% or more of our common shares, including certain prescribed public disclosure of their intentions for their holdings. Canadian securities laws also govern how any offer to acquire 20% or more of our equity or voting shares must be conducted. The foregoing is a limited and general summary of certain aspects of applicable securities law in the provinces and territories of Canada, all in effect as of the date hereof. This summary is not a comprehensive description of relevant or applicable considerations regarding such requirements and, accordingly, is not intended to be, and should not be interpreted as, legal advice to any prospective purchaser and no representation with respect to such requirements to any prospective purchaser is made. Prospective investors should consult their own Canadian legal advisors with respect to any questions regarding securities law in the provinces and territories of Canada.

Indemnification of Directors and Officers

Under the BC Act, we may indemnify a present or former director or officer or a person who acts or acted at our request as a director or officer of another corporation or one of our affiliates, and his or her heirs and personal representatives, against all costs, charges and expenses, including legal and other fees and amounts paid to settle an action or satisfy a judgment, actually and reasonably incurred by him or her including an amount paid to settle an action or satisfy a judgment in respect of any legal proceeding or investigative action to which he or she is made a party by reason of his or her position and provided that the director or officer acted honestly and in good faith with a view to the best interests of Atlantic Power Corporation or such other corporation, and, in the case of a criminal or administrative action or proceeding, had reasonable grounds for believing that his or her conduct was lawful. Other forms of indemnification may be made with court approval.

In accordance with our Articles, we shall indemnify every director or former director, or may, subject to the BC Act, indemnify any other person. We have entered into indemnity agreements with our directors and executive officers, whereby we have agreed to indemnify the directors and officers to the extent permitted by our Articles and the BC Act.

Our Articles permit us, subject to the limitations contained in the BC Act, to purchase and maintain insurance on behalf of any person, as the board of directors may from time to time determine. Our directors and officers liability insurance coverage consists of three policies with aggregate limits of $50 million.

Transfer agent and registrar

Computershare Investor Services Inc. and Computershare Trust Company, N.A. serve as our transfer agents and registrars for our common shares.

Description of Debt Securities

We may offer secured or unsecured debt securities in one or more series which may be senior, subordinated or junior subordinated, and which may be convertible into another security.

The following description briefly sets forth certain general terms and provisions of the debt securities. The particular terms of the debt securities offered by any prospectus supplement and the

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extent, if any, to which these general provisions may apply to the debt securities, will be described in the applicable prospectus supplement. We may issue debt securities in one or more series under the trust indenture, dated as of December 17, 2009, between us and Computershare Trust Company of Canada, as trustee. We may issue debt securities in one or more series under a New York law indenture to be entered into between us and a trustee to be named in the indenture. The form of the New York indenture is attached as an exhibit to the registration statement of which this prospectus forms a part. We use the term "indentures" to refer to both the Canadian indenture and the New York indenture, and we use the term "trustee" to refer to the trustee under either indenture, as applicable. The indentures will be qualified under the Trust Indenture Act of 1939 (the "TIA"). The terms of the debt securities will include those set forth in the applicable indenture and those made a part of the indenture by the TIA. You should read the summary below, the applicable prospectus supplement and the provisions of the applicable indenture and indenture supplement, if any, in their entirety before investing in our debt securities.

The aggregate principal amount of debt securities that may be issued under the indentures is unlimited. The prospectus supplement relating to any series of debt securities that we may offer will contain the specific terms of the debt securities. These terms may include the following:

•: the title and aggregate principal amount of the debt securities and any limit on the aggregate principal amount;
•: whether the debt securities will be senior, subordinated or junior subordinated;
•: whether the debt securities will be secured or unsecured;
•: any applicable subordination provisions for any subordinated debt securities;
•: the maturity date(s) or method for determining same;
•: the interest rate(s) or the method for determining same;
•: the dates on which interest will accrue or the method for determining dates on which interest will accrue and dates on which interest will be payable and whether interest shall be payable in cash or additional securities;
•: whether the debt securities are convertible or exchangeable into other securities and any related terms and conditions;
•: redemption or early repayment provisions;
•: authorized denominations;
•: if other than the principal amount, the principal amount of debt securities payable upon acceleration;
•: place(s) where payment of principal and interest may be made, where debt securities may be presented and where notices or demands upon the company may be made;
•: whether such debt securities will be issued in whole or in part in the form of one or more global securities and the date as which the securities are dated if other than the date of original issuance;
•: amount of discount or premium, if any, with which such debt securities will be issued;
•: any covenants applicable to the particular debt securities being issued;
•: any additions or changes in the defaults and events of default applicable to the particular debt securities being issued;

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•: the guarantors of each series, if any, and the extent of the guarantees (including provisions relating to seniority, subordination, security and release of the guarantees), if any;
•: the currency, currencies or currency units in which the purchase price for, the principal of and any premium and any interest on, such debt securities will be payable;
•: the time period within which, the manner in which and the terms and conditions upon which the holders of the debt securities or the company can select the payment currency;
•: our obligation or right to redeem, purchase or repay debt securities under a sinking fund, amortization or analogous provision;
•: our obligation or right to redeem, purchase or repay debt securities under a sinking fund, amortization or analogous provision;
•: any restriction or conditions on the transferability of the debt securities;
•: provisions granting special rights to holders of the debt securities upon occurrence of specified events;
•: additions or changes relating to compensation or reimbursement of the trustee of the series of debt securities;
•: additions or changes to the provisions for the defeasance of the debt securities or to provisions related to satisfaction and discharge of the indenture;
•: whether and under what circumstances we will pay additional amounts to non-Canadian holders in respect of any tax assessment or government charge, and, if so, whether we will have the option to redeem the debt securities rather than pay such additional amounts;
•: provisions relating to the modification of the indenture both with and without the consent of holders of debt securities issued under the indenture and the execution of supplemental indentures for such series; and
•: any other terms of the debt securities (which terms shall not be inconsistent with the provisions of the TIA, but may modify, amend, supplement or delete any of the terms of the indenture with respect to such series debt securities).

We may sell the debt securities, including original issue discount securities, at par or at a substantial discount below their stated principal amount. Unless we inform you otherwise in a prospectus supplement, we may issue additional debt securities of a particular series without the consent of the holders of the debt securities of such series or any other series outstanding at the time of issuance. Any such additional debt securities, together with all other outstanding debt securities of that series, will constitute a single series of securities under the applicable indenture.

We will describe in the applicable prospectus supplement any other special considerations for any debt securities we sell which are denominated in a currency or currency unit other than U.S. dollars. In addition, debt securities may be issued where the amount of principal and/or interest payable is determined by reference to one or more currency exchange rates, commodity prices, equity indices or other factors. Holders of such securities may receive a principal amount or a payment of interest that is greater than or less than the amount of principal or interest otherwise payable on such dates, depending upon the value of the applicable currencies, commodities, equity indices or other factors. Information as to the methods for determining the amount of principal or interest, if any, payable on any date, the currencies, commodities, equity indices or other factors to which the amount payable on such date is linked.

Material United States and Canadian federal income tax consequences and special considerations, if any, applicable to any such series will be described in the applicable prospectus supplement.

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Debt Securities Issued under the Canadian Indenture

The following summary description sets forth some of the general terms and provisions of the Canadian indenture. Because this is a summary description, it does not contain all of the information that may be important to you and is qualified in its entirety by reference to the Canadian indenture, any supplement to the Canadian indenture under which debt securities are issued ("Canadian Debt Securities") and the form of the Canadian Debt Securities as filed with securities regulators in Canada and the United States.

General

Canadian Debt Securities issued under and pursuant to the provisions of the Canadian indenture, as supplemented by a supplement (each, a "supplemental indenture") will be issuable only in denominations of $1,000 and integral multiples thereof, unless otherwise specified in such supplemental indenture. At the closing of the applicable offering, the Canadian Debt Securities will be available for delivery in book-entry form only through the facilities of CDS Clearing and Depository Services Inc. ("CDS"). Holders of beneficial interests in the Canadian Debt Securities will not have the right to receive physical certificates evidencing their ownership of Canadian Debt Securities except under certain circumstances described under "Description of Canadian Debt Securities—Book entry, delivery and form." No fractional Canadian Debt Securities will be issued.

The interest on the Canadian Debt Securities will be payable in lawful money of Canada, unless otherwise specified in the applicable supplemental indenture. Subject to any required regulatory approval and provided no event of default has occurred and is continuing, the Company shall have the option to pay such interest by delivering a number of common shares to an agent for sale, in which event holders of the Canadian Debt Securities will be entitled to receive a cash payment equal to the interest owed from the proceeds of the sale of the requisite number of common shares by the agent. The Canadian indenture does not, and any supplemental indenture will not, contain a requirement for the Company to increase the amount of interest or other payments to holders of Canadian Debt Securities should the Company become required to withhold amounts in respect of income or similar taxes on payment of interest or other amounts.

The principal on the Canadian Debt Securities will be payable in lawful money of Canada, unless otherwise specified in the applicable supplemental indenture, or, at the option of the Company and subject to applicable regulatory approval, by delivery of common shares to satisfy in whole or in part its obligation to repay the principal under the Canadian Debt Securities as further described under "Description of Canadian Debt Securities—Payment upon redemption or maturity" and "Description of Canadian Debt Securities—Redemption and purchase."

The Canadian Debt Securities will be direct obligations of the Company and will not be secured by any mortgage, pledge, hypothec or other charge and will be subordinated to other liabilities of the Company as described under "Description of Canadian Debt Securities—Subordination."

The Canadian indenture does not, and any supplemental indenture will not, restrict the Company from incurring additional indebtedness for borrowed money or from mortgaging, pledging or charging its assets to secure any indebtedness. The Canadian Debt Securities will be transferable, and may be presented for conversion, at the principal offices of the Debenture Trustee in Toronto, Ontario.

Conversion Privilege

The Canadian Debt Securities may, if so provided in the applicable supplemental indenture, be convertible at the holder's option into fully paid, non-assessable and freely-tradeable common shares at any time prior to the close of business on the earlier of the specified maturity date and the last business day immediately preceding the date specified by the Company for redemption of the Canadian

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Debt Securities, at a specified conversion price. No adjustment will be made for dividends or distributions payable on common shares issuable upon conversion; however, holders converting their Canadian Debt Securities shall be entitled to receive, in addition to the applicable number of common shares, accrued and unpaid interest in respect thereof for the period up to but excluding the date of conversion from the latest interest payment date.

Subject to the provisions thereof, the Canadian indenture provides for the adjustment of the conversion rights in certain events including: (i) the subdivision or consolidation of the outstanding common shares; (ii) the issue of common shares or securities convertible into common shares by way of stock dividend or other distribution; (iii) the issuance of options, rights or warrants to all or substantially all the holders of common shares entitling them to acquire common shares or other securities convertible into common shares at less than 95% of the then current market price of the common shares; and (iv) the distribution to all or substantially all holders of common shares of any securities or assets (other than cash dividends and equivalent dividends in securities paid in lieu of cash dividends in the ordinary course).

Provided the common shares are then listed on the TSX and/or the NYSE, the term "current market price" will mean the volume weighted average price of the common shares on the TSX or the NYSE, as the case may be, for the 20 consecutive trading days ending on the fifth trading day preceding the date of the applicable event, as specified in the applicable supplemental indenture in respect of the Canadian Debt Securities issued thereunder.

There will be no adjustment of the conversion price in respect of any event described in (ii), (iii) or (iv) above if, subject to prior regulatory approval, if required, the holders of the Canadian Debt Securities are allowed to participate as though they had converted their Canadian Debt Securities prior to the applicable record date or effective date. The Company will not be required to make adjustments in the conversion price unless the cumulative effect of such adjustments would change the conversion price by at least 1%. In the case of any reclassification of the common shares or a capital reorganization of the Company (other than as described in (i) or (ii) above) or in case of any amalgamation, arrangement or merger of the Company with or into any other entity, or in the case of any sale or conveyance of the properties and assets of the Company as, or substantially as, an entirety to any other entity, or a liquidation, dissolution or winding-up of the Company, the terms of the conversion privilege shall be adjusted so that each Canadian Debt Security shall, after such reclassification, capital reorganization, consolidation, amalgamation, arrangement or merger, sale or conveyance or liquidation, dissolution or winding-up or other similar transaction, be exercisable, in lieu of common shares, for the kind and amount of securities or property of the Company, or such continuing, successor or purchaser entity, as the case may be, which the holder thereof would have been entitled to receive as a result of such reclassification, capital reorganization, consolidation, amalgamation, arrangement or merger, sale or conveyance or liquidation, dissolution or winding-up or other similar transaction if on the effective date thereof it had been the holder of the number of common shares into which the Canadian Debt Security was convertible prior to the effective date of such reclassification, capital reorganization, consolidation, amalgamation, arrangement or merger, sale or conveyance or liquidation, dissolution or winding-up or other similar transaction. For example, if the Company were to sell all of its properties and assets for cash consideration, any Canadian Debt Securities that remain outstanding following such sale would then be convertible into cash, in an amount per common share otherwise issuable upon conversion of the Canadian Debt Security equal to the cash consideration per common share received by the holders of common shares pursuant to such sale.

No fractional common shares will be issued on any conversion of the Canadian Debt Securities, but in lieu thereof, the Company shall satisfy such fractional interest by a cash payment equal to the current market price of such fractional interest. Upon conversion, the Company may offer, and the

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converting holder may agree to, the delivery of cash for all or a portion of the Canadian Debt Securities surrendered in lieu of common shares.

Redemption and Purchase

The Canadian Debt Securities may not be redeemable by the Company on or before the date specified. See "Description of Canadian Debt Securities—Repurchase upon a change of control." During specified periods, the Canadian Debt Securities may be redeemed at the option of the Company, in whole at any time or in part from time to time, on not more than 60 days and not less than 30 days prior notice, at specified redemption price(s) with or without specified conditions, including, for example, that the volume weighted average price of the common shares on the TSX or the NYSE, as the case may be, for the 20 consecutive trading days ending on the fifth trading day preceding the date on which notice of redemption is given is not less than a specified percentage of the conversion price.

In the case of redemption of less than all of the Canadian Debt Securities, the Canadian Debt Securities to be redeemed will be selected by the Debenture Trustee on a pro rata basis or in such other manner as the Debenture Trustee deems equitable, subject to the consent of the TSX.

The Company will have the right to purchase Canadian Debt Securities in the market, by tender or by private contract subject to regulatory requirements; provided, however, that if an event of default (as defined herein) has occurred and is continuing, the Company will not have the right to purchase the Canadian Debt Securities by private contract.

Payment upon Redemption or Maturity

On redemption (the "Redemption Date") or on the maturity date, the Company will repay the indebtedness represented by the Canadian Debt Securities by paying to the Debenture Trustee in lawful money of Canada, unless another currency is specified in the applicable supplemental indenture, an amount equal to the redemption price or principal amount of the outstanding Canadian Debt Securities, together with accrued and unpaid interest thereon, respectively. The Company may, at its option, on not more than 60 days and not less than 40 days prior notice and subject to any required regulatory approvals, unless an event of default has occurred and is continuing, elect to satisfy its obligation to repay, in whole or in part, the principal amount of the Canadian Debt Securities which are to be redeemed or which have matured by issuing and delivering freely tradeable common shares to the holders of the Canadian Debt Securities. The number of common shares to be issued will be determined by dividing the principal amount of the Canadian Debt Securities which are to be redeemed or have matured by a specified percentage of the current market price of the common shares on the Redemption Date or maturity date, as the case may be.

No fractional common shares will be issued to holders of Canadian Debt Securities, but in lieu thereof, the Company shall satisfy such fractional interest by a cash payment equal to the current market price of such fractional interest.

The delivery of common shares to satisfy the Company's obligations under the Canadian Debt Securities may require regulatory approval, including filing a prospectus qualifying the distribution of such common shares or obtaining an exemptive relief order from the relevant Canadian securities regulators in the event that an exemption from the prospectus and registration requirements of applicable Canadian securities laws is not available at the time of the delivery of common shares. In addition, any issuance of common shares to satisfy the Company's obligations under the Canadian Debt Securities will be subject to the approval of the TSX and the NYSE (and any other exchange on which the common shares are listed at the relevant time).

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Cancellation

All Canadian Debt Securities converted, redeemed or purchased will be cancelled and may not be reissued or resold.

Subordination

The payment of the principal of, and interest on, the Canadian Debt Securities will be subordinated in right of payment, in the circumstances referred to below and more particularly as set forth in the Canadian indenture, to the prior payment in full of all existing and future Senior Indebtedness of the Company, including our revolving credit facility, the convertible debentures of the Company issued on October 11, 2006 and our senior notes issued on November 4, 2011. "Senior Indebtedness" of the Company is defined in the Canadian indenture and includes: (a) indebtedness of the Company for borrowed money; (b) obligations of the Company evidenced by bonds, debentures, notes or other similar instruments; (c) obligations of the Company arising pursuant or in relation to bankers' acceptances, letters of credit and letters of guarantee (including payment and reimbursement obligations in respect thereof) or indemnities issued in connection therewith; (d) obligations of the Company under any swap, hedging or other similar contracts or arrangements; (e) obligations of the Company under guarantees, indemnities, assurances, legally binding comfort letters or other contingent obligations relating to the Senior Indebtedness or other obligations of any other person which would otherwise constitute Senior Indebtedness within the meaning of this definition, including the guarantee of the Company's revolving credit facility; (f) all indebtedness of the Company representing the deferred purchase price of any property including, without limitation, purchase money mortgages; (g) accounts payable to trade creditors; (h) all renewals, extensions and refinancing of any of the foregoing; and (i) all costs and expenses incurred by or on behalf of the holder of any Senior Indebtedness in enforcing payment or collection of any such Senior Indebtedness, including enforcing any security interest securing the same. The Canadian Debt Securities will be effectively structurally subordinate to claims of creditors (including trade creditors) of the Company's subsidiaries, including Atlantic Power Holdings, Inc. ("Holdings"). As of August 6, 2012, we had an aggregate amount of $524.7 million of Senior Indebtedness outstanding.

The 6.25% convertible debentures we issued on December 17, 2009, the 5.60% convertible debentures we issued on October 20, 2010, the 5.75% convertible debentures we issued on July 5, 2012 and any Canadian Debt Securities issued under the Canadian indenture or under any supplemental indenture will rank pari passu with each other (regardless of their actual date or terms of issue).

The Canadian indenture provides that in the event of any insolvency or bankruptcy proceedings, or any receivership, liquidation or reorganization or other similar proceedings relating to the Company, or to its property or assets, or in the event of any proceedings for voluntary liquidation, dissolution or other winding-up of the Company, whether or not involving insolvency or bankruptcy, or any marshalling of the assets and liabilities of the Company, then holders of Senior Indebtedness will receive payment in full before the holders of Canadian Debt Securities will be entitled to receive any payment or distribution of any kind or character, whether in cash, property or securities, which may be payable or deliverable in any such event in respect of any of the Canadian Debt Securities or any unpaid interest accrued thereon.

The Canadian indenture also provides that the Company will not make any payment, and the holders of the Canadian Debt Securities will not be entitled to demand, institute proceedings for the collection of, or receive any payment or benefit (including, without any limitation, by set-off, combination of accounts or otherwise in any manner whatsoever) on account of indebtedness represented by the Canadian Debt Securities at any time when a default or an event of default has occurred with respect to any Senior Indebtedness permitting a senior creditor to demand payment or accelerate the maturity thereof and the notice of such default or event of default has been given by or

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on behalf of holders of Senior Indebtedness to the Company or the Company otherwise has knowledge thereof, unless such notice has been revoked, such default or event of default has been cured or the Senior Indebtedness has been repaid or satisfied in full as defined in the Canadian indenture.

The Debenture Trustee and the Company will also be authorized (and obligated upon any request from certain holders of Senior Indebtedness) under the Canadian indenture to enter into subordination agreements on behalf of the holders of Canadian Debt Securities with any holder of Senior Indebtedness.

Repurchase upon a Change of Control

Upon the occurrence of a change of control of the Company, the holders of the Canadian Debt Securities will have the right to require the Company to repurchase their Canadian Debt Securities, in whole or in part at a price equal to 100% of the principal amount thereof (the "Offer Price") plus accrued and unpaid interest thereon. A change of control will be deemed to occur upon: (i) an acquisition by a person or group of persons acting jointly or in concert (within the meaning of the Securities Act (Ontario)) of ownership of, or voting control or direction over, 50% or more of the common shares; or (ii) the sale or other transfer of all or substantially all of the consolidated assets of the Company.

A change of control will not include a sale, merger, reorganization, or other similar transaction if the previous holders of the common shares hold at least 50% of the voting control in such merged, reorganized or other continuing entity.

If 90% or more of the aggregate principal amount of the Canadian Debt Securities outstanding on the date of the giving of notice of the change of control have been tendered for purchase following a change of control, the Company will have the right to redeem all the remaining Canadian Debt Securities on the purchase date, together with accrued and unpaid interest to such date. Notice of such redemption must be given to the Debenture Trustee by the Company within 10 days following expiry of the right to require repurchase after the change of control and, as soon as possible thereafter, by the Debenture Trustee to the holders of the Canadian Debt Securities not tendered for purchase.

The Canadian indenture contains notification provisions to the effect that:

(a) the Company will promptly give written notice to the Debenture Trustee of the occurrence of a change of control and the Debenture Trustee will thereafter give to the holders of Canadian Debt Securities a notice of the change of control, the right of the holders of Canadian Debt Securities to require repurchase and the right of the Company to redeem untendered Canadian Debt Securities under certain circumstances; and

(b) a holder of Canadian Debt Securities, to exercise the right to require repurchase following the change of control, must deliver to the Debenture Trustee, not less than five business days prior to the date which is 30 days after the date the Debenture Trustee delivers notice of the change of control to the holders of Canadian Debt Securities, written notice of the holder's exercise of the right to require repurchase, together with a duly endorsed form of transfer.

The Company will comply with the requirements of Canadian securities laws and regulations to the extent such laws and regulations are applicable in connection with the repurchase of the Canadian Debt Securities in the event of a change of control.

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Cash Change of Control

In addition to the requirement for the Company to repurchase Canadian Debt Securities following a change of control, if a change of control occurs in which 10% or more of the consideration for the common shares in the transaction or transactions constituting a change of control consists of:

•: cash, other than cash payments for fractional common shares and cash payments made in respect of dissenter's appraisal rights;
•: equity securities that are not traded or intended to be traded immediately following such transactions on a stock exchange; or
•: other property that is not traded or intended to be traded immediately following such transactions on a stock exchange,

then subject to regulatory approvals, during the period beginning ten trading days before the anticipated date on which the change of control becomes effective and ending 30 days after the notice of change of control and offer to repurchase Canadian Debt Securities is delivered, holders of Canadian Debt Securities will be entitled to convert their Canadian Debt Securities, subject to certain limitations, and receive, in addition to the number of common shares they would otherwise be entitled to receive as set forth under "Description of Canadian Debt Securities—Conversion privilege" above, an additional number of common shares per $1,000 principal amount of Canadian Debt Securities (the "Make Whole Premium Shares") to be specified in the applicable supplemental indenture. Any such additional conversion entitlement shall be subject to the change of control transaction having been completed. The Make Whole Premium Shares and the determination thereof will be adjusted in a similar manner as the conversion rate set forth above under "Description of Canadian Debt Securities—Conversion Privilege".

Modification

The rights of the Canadian Debt Security holders that have been or may be issued under the Canadian indenture or any supplemental indenture may be modified in accordance with the terms of the Canadian indenture. For that purpose, among others, the Canadian indenture contains certain provisions which make binding on all Canadian Debt Security holders resolutions passed at meetings of the Canadian Debt Security holders by votes cast thereat by holders of not less than 66²/3 of the principal amount of the then outstanding Canadian Debt Securities present at the meeting or represented by proxy, or rendered by instruments in writing signed by the holders of not less than 66²/3% of the principal amount of the then outstanding Canadian Debt Securities. In certain cases, the modification will, instead or in addition, require assent by the holders of the required percentage of each particularly affected series of debentures, as the case may be. Under the Canadian indenture, certain amendments may be made to the Canadian indenture without the consent of the Canadian Debt Security holders.

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Events of Default

The Canadian indenture provides that an event of default ("Event of Default") in respect of the Canadian Debt Securities will occur if certain events described in the Canadian indenture occur, including if any one or more of the following described events has occurred and is continuing with respect to the Canadian Debt Securities: (i) failure for 15 days to pay interest on the Canadian Debt Securities when due; (ii) failure to pay principal or premium, if any, on the Canadian Debt Securities, whether at maturity, upon redemption, by declaration or otherwise; or (iii) certain events of bankruptcy, insolvency or reorganization of the Company under bankruptcy or insolvency laws. If an Event of Default has occurred and is continuing, the Debenture Trustee may, in its discretion, and shall, upon the request of holders of not less than 25% in principal amount of the then outstanding Canadian Debt Securities, declare the principal of (and premium, if any) and interest on all outstanding Canadian Debt Securities to be immediately due and payable.

Offers for Canadian Debt Securities

The Canadian indenture contains provisions to the effect that if an offer is made for the Canadian Debt Securities which is a take-over bid for Canadian Debt Securities within the meaning of the Securities Act (Ontario) and not less than 90% of the Canadian Debt Securities (other than Canadian Debt Securities held at the date of the take-over bid by or on behalf of the offeror or associates or affiliates of the offeror) are taken up and paid for by the offeror, the offeror will be entitled to acquire the Canadian Debt Securities held by Canadian Debt Security holders who did not accept the offer on the terms offered by the offeror.

Book Entry, Delivery and Form

Canadian Debt Securities will be issued in the form of fully registered global Canadian Debt Securities (the "Global Debentures") held by, or on behalf of, CDS or its successor (the "Depository"), as custodian for its participants.

All Canadian Debt Securities will be represented in the form of Global Debentures registered in the name of the Depository or its nominee. Purchasers of Canadian Debt Securities represented by Global Debentures will not receive Canadian Debt Securities in definitive form. Rather, the Canadian Debt Securities will be represented only in "book-entry only" form (unless the Company, in its sole discretion, elects to prepare and deliver definitive Canadian Debt Securities in fully registered form). Beneficial interests in the Global Debentures, constituting ownership of the Canadian Debt Securities, will be represented through book-entry accounts of institutions (including the underwriters) acting on behalf of beneficial owners, as direct and indirect participants of the Depository (the "participants"). Each purchaser of a Canadian Debt Security represented by a Global Debenture will receive a customer confirmation of purchase from the underwriters or registered dealer from whom the Canadian Debt Security is purchased in accordance with the practices and procedures of the selling underwriters or registered dealer. The practices of registered dealers may vary, but generally customer confirmations are issued promptly after execution of a customer order. The Depository will be responsible for establishing and maintaining book-entry accounts for its participants having interests in Global Debentures.

If the Depository notifies the Company that it is unwilling or unable to continue as depository in connection with the Global Debentures, or if at any time the Depository ceases to be a clearing agency or otherwise ceases to be eligible to be a depository and the Company and the Debenture Trustee are unable to locate a qualified successor, or if the Company elects, in its sole discretion, to terminate the book-entry system, with the consent of the Debenture Trustee, or if under certain circumstances described in the Canadian indenture, an Event of Default has occurred, beneficial owners of Canadian Debt Securities represented by Global Debentures at such time will receive Canadian Debt Securities in registered and definitive form (the "Definitive Debentures").

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Transfer and Exchange of Canadian Debt Securities

Transfers of beneficial ownership in Canadian Debt Securities represented by Global Debentures will be effected through records maintained by the Depository for such Global Debentures or its nominees (with respect to interests of participants) and on the records of participants (with respect to interests of persons other than participants). Unless the Company elects, in its sole discretion, to prepare and deliver Definitive Debentures, beneficial owners who are not participants in the Depository's book-entry system, but who desire to purchase, sell or otherwise transfer ownership of or other interests in Global Debentures, may do so only through participants in the Depository's book-entry system.

The ability of a beneficial owner of an interest in a Canadian Debt Security represented by a Global Debenture to pledge the Canadian Debt Security or otherwise take action with respect to such owner's interest in a Canadian Debt Security represented by a Global Debenture (other than through a participant) may be limited due to the lack of a physical certificate.

Registered holders of Definitive Debentures may transfer such Canadian Debt Securities upon payment of taxes or other charges incidental thereto, if any, by executing and delivering a form of transfer together with the Canadian Debt Securities to the registrar for the Canadian Debt Securities at its principal offices in Toronto, Ontario or such other city or cities as may from time to time be designated by the Company, whereupon new Canadian Debt Securities will be issued in authorized denominations in the same aggregate principal amount as the Canadian Debt Securities so transferred, registered in the names of the transferees. No transfer of a Canadian Debt Security will be registered on any interest payment date or during the five business days preceding an interest payment date on the Canadian Debt Securities or on any Redemption Date or during the five business days preceding the Redemption Date.

Payments

Payments of interest and principal on each Global Debenture will be made to the Depository or its nominee, as the case may be, as the registered holder of the Global Debenture. As long as the Depository or its nominee is the registered owner of a Global Debenture, such Depository or its nominee, as the case may be, will be considered the sole legal owner of the Global Debenture for the purposes of receiving payments of interest and principal on the Canadian Debt Securities and for all other purposes under the Canadian indenture and the Canadian Debt Securities. The record date for the payment of interest will be the fifth business day prior to the applicable interest payment date. Interest payments on Global Debentures will be made by electronic funds transfer or by cheque on the day interest is payable and delivered to the Depository or its nominee, as the case may be.

The Company understands that the Depository or its nominee, upon receipt of any payment of interest or principal in respect of a Global Debenture, will credit participants' accounts, on the date interest or principal is payable, with payments in amounts proportionate to their respective beneficial interest in the principal amount of such Global Debenture as shown on the records of the Depository or its nominee. The Company also understands that payments of interest and principal by participants to the owners of beneficial interests in such Global Debenture held through such participants will be governed by standing instructions and customary practices, as is the case with securities held for the accounts of customers in bearer form or registered in "street name" and will be the responsibility of such participants. The responsibility and liability of the Company in respect of payments on Debentures represented by the Global Debenture is limited solely and exclusively, while the Canadian Debt Securities are registered in Global Debenture form, to making payment of any interest and principal due on such Canadian Debt Securities to the Depository or its nominee.

If Definitive Debentures are issued instead of or in place of Global Debentures, payments of interest on each Definitive Debenture will be made by electronic funds transfer, if agreed to by the

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holder of the Definitive Debenture, or by cheque dated the interest payment date and mailed to the address of the holder appearing in the register maintained by the registrar for the Canadian Debt Securities at least one business day prior to the applicable interest payment date. Payment of principal at maturity will be made at the principal office of the paying agent in the City of Toronto (or in such other city or cities as may from time to time be designated by the Company) against surrender of the Definitive Debentures, if any.

Reports to Holders

The Company shall file with the Debenture Trustee copies of the Company's annual report and other documents that the Company is required to deliver to shareholders under applicable securities legislation.

Governing Law

Each of the Canadian indenture, any supplemental indenture and the Canadian Debt Securities will be governed by, and construed in accordance with, the laws of the Province of Ontario and the federal laws of Canada applicable therein applicable to contracts executed and to be performed entirely in such Province.

Debt Securities Issued under the New York Indenture

The following summary description sets forth some of the general terms and provisions of the New York indenture. Because this is a summary description, it does not contain all of the information that may be important to you and is qualified in its entirety by reference to the New York indenture, any supplement to the New York indenture under which debt securities are issued ("US Debt Securities") and the form of any such US Debt Securities as filed with securities regulators in Canada and the United States.

General

We may sell the US Debt Securities, including original issue discount securities, at par or at a substantial discount below their stated principal amount. Unless we inform you otherwise in a prospectus supplement, we may issue additional US Debt Securities of a particular series without the consent of the holders of such series outstanding at the time of issuance. Any such additional US Debt Securities, together with all other outstanding debt securities of that series, will constitute a single series of securities under the New York indenture. In addition, we will describe in the applicable prospectus supplement, material United States ("U.S.") federal tax considerations and any other special considerations for any US Debt Securities we sell which are denominated in a currency or currency unit other than U.S. dollars. Any taxes withheld or deducted from payments in respect of the US Debt Securities and paid to the relevant tax authority shall be deemed to have been paid to the applicable holder. Unless we inform you otherwise in the applicable prospectus supplement, the US Debt Securities will not be listed on any securities exchange.

We expect most US Debt Securities to be issued in fully registered form without coupons and in denominations of $1,000 and any integral multiples thereof. Subject to the limitations provided in the New York indenture and in the applicable prospectus supplement, US Debt Securities that are issued in registered form may be transferred or exchanged at the corporate office of the trustee or the principal corporate trust office of the trustee, without the payment of any service charge, other than any tax or other governmental charge payable in connection therewith.

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Global Securities

Unless we inform you otherwise in the applicable prospectus supplement, the US Debt Securities of a series may be issued in whole or in part in the form of one or more global securities that will be deposited with, or on behalf of, a depositary identified in the applicable prospectus supplement. Global securities will be issued in registered form and in either temporary or definitive form. Unless and until it is exchanged in whole or in part for the individual US Debt Securities, a global security may not be transferred except as a whole by the depositary for such global security to a nominee of such depositary or by a nominee of such depositary to such depositary or another nominee of such depositary or by such depositary or any such nominee to a successor of such depositary or a nominee of such successor. The specific terms of the depositary arrangement with respect to any US Debt Securities of a series and the rights of and limitations upon owners of beneficial interests in a global security will be described in the applicable prospectus supplement.

Events of Default

Under the terms of the New York indenture, each of the following constitutes an event of default for a series of US Debt Securities unless it is either inapplicable to a particular series or it is specifically deleted or modified:

•: default for 30 days in the payment of any interest when due;
•: default in the payment of principal, or premium, if any, when due;
•: default for 30 days in the payment of any sinking fund installment, if any, when due;
•: default in the performance, or breach, of any covenant or agreement in the New York indenture for 90 days after written notice;
•: default in the payment of any principal of any of our indebtedness for money borrowed (other than any indebtedness owing to any of our subsidiaries) in a principal amount in excess of $50,000,000 (or the foreign currency equivalent at the time) at the stated final maturity thereof or the occurrence of any other default resulting in the acceleration prior to the stated maturity thereof, if such indebtedness is not discharged or such acceleration is not rescinded or annulled within 30 days after written notice to us by the trustee or to us and the trustee by the holders of not less than 25% in principal amount of the applicable series then outstanding, provided that the resulting event of default under the New York indenture with respect to such series will be deemed cured or waived, without any further action by us or any other person, if such other default is cured by us or waived by the holders of such indebtedness;
•: certain events of bankruptcy, insolvency or reorganization; and
•: any other event of default described in the applicable company order or supplemental indenture under which the series of US Debt Securities is issued.

We are required to furnish the trustee annually with an officer's certificate as to our compliance with all conditions and covenants under the New York indenture. The New York indenture provides that the trustee may withhold notice to you of any default, except in respect of the payment of the principal of, premium, if any, or interest on the US Debt Securities, if it considers it in the interests of the holders of the US Debt Securities to do so.

Effect of an Event of Default

If an event of default exists (other than an event of default in the case of certain events of bankruptcy), the trustee or the holders of not less than 25% in aggregate principal amount of a series of outstanding US Debt Securities may declare the principal amount, or, if the US Debt Securities are

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original issue discount securities, the portion of the principal amount as may be specified in the terms of that series, of and all accrued but unpaid interest on all outstanding US Debt Securities of that series to be due and payable immediately, by a notice in writing to us, and to the trustee if given by holders. Upon that declaration the principal (or specified) amount will become immediately due and payable. However, at any time after a declaration of acceleration has been made, but before a judgment or decree for payment of the money due has been obtained, the event of default may, without further act, be deemed to have been waived and such declaration may, without further act, be deemed to have been rescinded and annulled subject to conditions specified in the New York indenture.

If an event of default in the case of certain events of bankruptcy, insolvency or reorganization exists, the principal amount of all US Debt Securities outstanding under the New York indenture shall automatically, and without any declaration or other action on the part of the trustee or any holder of such outstanding debt, become immediately due and payable.

Subject to the provisions of the New York indenture relating to the duties of the trustee, if an event of default then exists, the trustee will be under no obligation to exercise any of its rights or powers under the New York indenture (other than the payment of any amounts on the US Debt Securities furnished to it pursuant to the New York indenture) at your (or any other person's) request, order or direction, unless you have (or such other person has) offered to the trustee reasonable security or indemnity. Subject to the provisions for the security or indemnification of the trustee, the holders of a majority in aggregate principal amount of a series of outstanding US Debt Securities have the right to direct the time, method and place of conducting any proceeding for any remedy available to the trustee, or exercising any trust or power conferred on the trustee in connection with the US Debt Securities of that series.

Legal Proceedings and Enforcement of Right to Payment

You will not have any right to institute any proceeding in connection with the New York indenture or for any remedy under the New York indenture, unless you have previously given to the trustee written notice of a continuing event of default with respect to US Debt Securities of that series. In addition, the holders of at least 25% in aggregate principal amount of a series of the outstanding US Debt Securities must have made written request, and offered reasonable security or indemnity, to the trustee to institute that proceeding as trustee, and, within 60 days following the receipt of that notice, the trustee must not have received from the holders of a majority in aggregate principal amount of the outstanding US Debt Securities of that series a direction inconsistent with that request, and must have failed to institute the proceeding. However, you will have an absolute and unconditional right to receive payment of the principal of, premium, if any, and interest on that debt security on or after the due dates expressed in the debt security and to institute a suit for the enforcement of that payment.

Modification and Waiver

Modification

We and the trustee may modify and amend the New York indenture with the consent of the holders of a majority in aggregate principal amount of the outstanding US Debt Securities of each series affected. However, no modification or amendment may, without the consent of the holder of each outstanding debt security affected:

•: extend the stated maturity of the principal of, or any installment of interest on, any outstanding debt security;
•: reduce the principal amount of or the interest on or any premium payable upon the redemption of any outstanding debt security;

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•: change the currency in which the principal amount of and premium, if any, or interest on any outstanding debt security is denominated or payable;
•: reduce the principal amount of an original issue discount security that would be due and payable upon a declaration of acceleration of the maturity thereof;
•: impair your right to institute suit for the enforcement of any payment on any outstanding debt security after the stated maturity or redemption date;
•: materially adversely affect the economic terms of any right to convert or exchange any outstanding debt security;
•: reduce the percentage of the holders of outstanding US Debt Securities necessary to modify or amend the New York indenture or to waive compliance with certain provisions of the New York indenture or certain defaults and consequences of such defaults; or
•: modify any of these provisions or any of the provisions relating to the waiver of certain past defaults or certain covenants, except to increase the required percentage to effect such action or to provide that certain other provisions may not be modified or waived without the consent of all of the holders of the US Debt Securities affected.

Waiver

The holders of a majority in aggregate principal amount of the outstanding US Debt Securities of a series may, on behalf of the holders of all US Debt Securities of that series, waive compliance by us with certain restrictive covenants of the New York indenture.

The holders of a majority in aggregate principal amount of the outstanding US Debt Securities of a series may, on behalf of the holders of all US Debt Securities of that series, generally waive any past default under the New York indenture and the consequences of such default. However, a default in the payment of the principal of, or premium, if any, or any interest on, any debt security of that series cannot be so waived.

Merger, Consolidation and Sale of Assets

We will not consolidate with or merge into any other entity or sell other than for cash or lease all or substantially all our assets to another entity, or purchase all or substantially all the assets of another entity, and no entity may consolidate with or merge into us, unless:

•: we will be the continuing entity in any merger or consolidation or the successor, transferee or lessee entity (if other than us) is a corporation organized and validly existing under the laws of any U.S. domestic jurisdiction and expressly assumes our obligations relating to the US Debt Securities;
•: immediately after such consolidation, merger, sale, lease or purchase, there exists no event of default, and no event which, after notice or lapse of time or both, would become an event of default; and
•: other conditions described in the New York indenture are met.

This covenant would not apply to a purchase by a subsidiary of all or substantially all of the assets of another entity.

Defeasance and Covenant Defeasance

The New York indenture provides that we may discharge all of our obligations with respect to any series of the US Debt Securities at any time, and that we may also be released from our obligations

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under certain covenants and from certain other obligations, including obligations imposed by a company order or supplemental indenture with respect to that series, if any, and elect not to comply with those sections and obligations without creating an event of default. Discharge under the first procedure is called "defeasance" and under the second procedure is called "covenant defeasance."

Defeasance or covenant defeasance may be effected only if:

•: we irrevocably deposit with the trustee money or U.S. government obligations or a combination thereof, as trust funds in an amount sufficient to pay and discharge each installment of principal of, premium, if any, and interest on, all outstanding US Debt Securities of that series;
•: no event of default under the New York indenture has occurred and is continuing on the date of such deposit, other than an event of default resulting from the borrowing of funds and the grant of any related liens to be applied to such deposit; and
•: we deliver to the trustee an opinion of counsel to the effect that (i) the holders of the US Debt Securities of that series will not recognize income, gain or loss for U.S. federal income tax purposes as a result of the deposit, defeasance and discharge or as a result of the deposit and covenant defeasance and (ii) the deposit, defeasance and discharge or the deposit and covenant defeasance will not otherwise alter those holders' U.S. federal income tax treatment of principal and interest payments on the US Debt Securities of that series and, in the case of a defeasance, this opinion is accompanied by a ruling to that effect received from or published by the Internal Revenue Service.

Payment; Exchange; Transfer

We will designate a place of payment where you can receive payment of the principal of and any premium and interest on the US Debt Securities or transfer the US Debt Securities. Even though we will designate a place of payment, we may elect to pay any interest on the US Debt Securities by mailing a check to the person listed as the owner of the US Debt Securities in the security register or by wire transfer to an account designated by that person in writing not less than ten days before the date of the interest payment. There will be no service charge for any registration of transfer or exchange of the US Debt Securities, but we may require you to pay any tax or other governmental charge payable in connection with a transfer or exchange of the US Debt Securities.

Governing Law

The New York indenture and the US Debt Securities shall be construed in accordance with and governed by the laws of the State of New York.

Concerning the Trustee

The trustee under the New York indenture will have all the duties and responsibilities of an indenture trustee specified in the TIA. The trustee is not required to expend or risk its own funds or otherwise incur financial liability in performing its duties or exercising its rights and powers if it reasonably believes that it is not reasonably assured of repayment or adequate indemnity.

Under applicable Canadian law, a Canadian licensed trust company may be required to be appointed as co-trustee under the New York indenture or any supplement to the New York indenture under which US Debt Securities are issued in connection with the issuance of any such US Debt Securities offered for sale in Canada and in the United States pursuant to this prospectus and a prospectus supplement. In such circumstances, we may make an application to the appropriate Canadian regulatory authorities prior to such issuance for exemptions from this and other requirements of Canadian law applicable to the indentures. If such relief is not sought or obtained, the applicable legislative requirements will be complied with at the time of the applicable offering.

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Plan of Distribution

We may sell securities to or through underwriters, and we may also sell securities directly to other purchasers or through dealers or agents. Unless otherwise indicated in a prospectus supplement or other offering materials, the obligations of any underwriters to purchase the securities will be subject to conditions precedent and these underwriters will be obligated to purchase all the securities if any are purchased.

The distribution of the securities may be effected from time to time in one or more transactions at a fixed price or prices which may be changed, at market prices prevailing at the time of sale, at prices related to these prevailing market prices or at negotiated prices. The prospectus supplement or other offering materials will describe the method of distribution of the securities.

In connection with the sale of securities, underwriters may receive compensation from us or from purchasers of securities for whom they may act as agents, in the form of discounts, concessions or commissions. Underwriters, dealers and agents that participate in the distribution of securities may be deemed to be underwriters, and any discounts or commissions received by them and any profit on the resale of securities by them may be deemed to be underwriting discounts and commissions under the Securities Act. Any underwriter, dealer or agent that will participate in the distribution of the securities will be identified, and any compensation it will receive will be described, in the prospectus supplement or other offering materials.

Under agreements which may be entered into by us, underwriters, dealers and agents who participate in the distribution of securities may be entitled to indemnification by us against some liabilities, including liabilities under the Securities Act, or to contribution with respect to payments which the underwriters, dealers or agents may be required to make relating to these liabilities. Any agreement in which we agree to indemnify underwriters, dealers and agents against civil liabilities will be described in the prospectus supplement or other offering materials.

If so indicated in a prospectus supplement or other offering materials, we will authorize dealers or other persons acting as our agent to solicit offers by some institutions to purchase securities from us pursuant to contracts providing for payment and delivery on a future date. Institutions with which these contracts may be made include commercial and savings banks, insurance companies, pension funds, investment companies, educational and charitable institutions and others.

Legal Matters

Unless otherwise indicated in the applicable prospectus supplement, certain legal matters as to US and New York law will be passed upon for us by Goodwin Procter LLP, Boston, Massachusetts. Certain legal matters as to Canadian law will be passed upon for us by Goodmans and Goodmans LLP. Legal counsel to any underwriters may pass upon legal matters for such underwriters.

Experts

Table of Contents

incorporated in reliance on the report (which contains an explanatory paragraph relating to the Chambers Cogeneration Limited Partnership restatement of its financial statements as described in the Restatement of Previously Issued Financial Statements section of Note 2 to the financial statements) of PricewaterhouseCoopers LLP, independent auditors, given on the authority of said firm as experts in auditing and accounting.

Dividend Reinvestment Plan

5,962,443 Common Shares

PROSPECTUS SUPPLEMENT

August 8, 2012