Sec Form 4 Filing - DUNCAN R FOSTER @ ATLANTIC POWER CORP - 2021-05-14

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person DUNCAN R FOSTER 2. Issuer Name and Ticker or Trading Symbol ATLANTIC POWER CORP [ AT] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O ATLANTIC POWER CORPORATION, 3 ALLIED DRIVE, SUITE 155 3. Date of Earliest Transaction (MM/DD/YY) 05/14/2021 (Street) DEDHAM, MA02026 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common shares 05/14/2021 J( 1 ) 15,105 D $ 3.03 0 D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Deferred share units ( 2 ) 05/14/2021 D( 3 ) 249,435 ( 2 ) ( 2 ) Common shares 249,435 $ 3.03 0 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other DUNCAN R FOSTER C/O ATLANTIC POWER CORPORATION 3 ALLIED DRIVE, SUITE 155 DEDHAM, MA02026 X Signatures /s John S. Miele, attorney-in-fact 05/19/2021 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Pursuant to the terms of the Arrangement Agreement dated January 14, 2021 (the "Agreement") by and among Atlantic Power Corporation (the "Company"), Atlantic Power Preferred Equity Ltd. ("APPEL"), Atlantic Power Limited Partnership, Tidal Power Holdings Limited and Tidal Power Aggregator, LP (together with Tidal Power Holdings Limited, the "Purchasers"), the Purchasers purchased each share of Company common stock, no par value (each, a "Common Share") at a price per share of US$3.03, net to the seller in cash, without interest thereon and less any required withholding taxes. ( 2 )Represents previously reported awards of deferred share units ("DSUs") granted under the Company's Deferred Share Unit Plan, which provide for the payment of all accrued DSUs to the reporting person following his or her termination as a director. Each DSU is equal to the economic equivalent of one Common Share. ( 3 )Pursuant to the terms of the Agreement, all outstanding awards of DSUs will be cancelled and each non-employee director holding such DSUs will be entitled to receive a cash payment from the Company equal to US$3.03 for each Common Share subject to his or her DSU awards, without interest and less any applicable withholding taxes.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

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