Exhibit 4.13

Third Supplemental Indenture

THIRD SUPPLEMENTAL INDENTURE (this “Supplemental Indenture”), dated as of February 22, 2012 among Atlantic Oklahoma Wind, LLC, a Delaware limited liability company (the “New Guarantor”), Atlantic Power Corporation (or its successor), a British Columbia corporation (“Atlantic Power”), the Guarantors (the “Existing Guarantors”) under the Indenture referred to below, and Wilmington Trust, National Association, as trustee under the Indenture referred to below (the “Trustee”).

W I T N E S S E T H:

WHEREAS Atlantic Power has heretofore executed and delivered to the Trustee an Indenture (as such may be amended from time to time, the “Indenture”), dated as of November 4, 2011, providing for the issuance of its 9% Senior Notes due 2018 (the “Notes”);

WHEREAS under certain circumstances Atlantic Power is required (or permitted) to cause the New Guarantor to execute and deliver to the Trustee a supplemental indenture pursuant to which the New Guarantor shall unconditionally guarantee all of Atlantic Power’s obligations under the Notes pursuant to a Guarantee on the terms and conditions set forth herein; and

WHEREAS pursuant to Section 8.01 of the Indenture, the Trustee, Atlantic Power and the Existing Guarantors are authorized to execute and deliver this Supplemental Indenture.

NOW THEREFORE, in consideration of the foregoing and for other good and valuable consideration, the receipt of which is hereby acknowledged, the New Guarantor, Atlantic Power, the Existing Guarantors and the Trustee mutually covenant and agree for the equal and ratable benefit of the Holders as follows:

1. Definitions.

(a) Capitalized terms used herein without definition shall have the meanings assigned to them in the Indenture.

(b) For all purposes of this Supplemental Indenture, except as otherwise herein expressly provided or unless the context otherwise requires: (i) the terms and expressions used herein shall have the same meanings as corresponding terms and expressions used in the Indenture; and (ii) the words “herein,” “hereof” and “hereby” and other words of similar import used in this Supplemental Indenture refer to this Supplemental Indenture as a whole and not to any particular section hereof.

2. Agreement to Guarantee. The New Guarantor hereby agrees, jointly and severally with all other Guarantors, to guarantee Atlantic Power’s obligations under the Notes and the Indenture on the terms and subject to the conditions set forth in Article 10 of the Indenture and to be bound by all other applicable provisions of the Indenture. From and after the date hereof, the New Guarantor shall be a Guarantor for all purposes under the Indenture and the Notes.

3. Ratification of Indenture; Supplemental Indentures Part of Indenture. Except as expressly amended hereby, the Indenture is in all respects ratified and confirmed and all the terms, conditions and provisions thereof shall remain in full force and effect. This Supplemental Indenture shall form a part of the Indenture for all purposes, and every Holder heretofore or hereafter authenticated and delivered shall be bound hereby.

4. Governing Law. THIS SUPPLEMENTAL INDENTURE SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK, AS APPLIED TO CONTRACTS MADE AND PERFORMED WITHIN THE STATE OF NEW YORK (INCLUDING, WITHOUT LIMITATION, SECTION 5-1401 OF THE NEW YORK GENERAL OBLIGATIONS LAW OR ANY SUCCESSOR STATUTE). EACH OF THE PARTIES HERETO AGREES TO SUBMIT TO

THE JURISDICTION OF THE COURTS OF THE STATE OF NEW YORK IN ANY ACTION OR PROCEEDING ARISING OUT OF OR RELATING TO THIS SUPPLEMENTAL INDENTURE.

5. Trustee Makes No Representation. The Trustee shall not be responsible in any manner whatsoever for or in respect of the validity or sufficiency of this Supplemental Indenture or for or in respect of the recitals contained herein, all of which are made solely by Atlantic Power.

6. Multiple Counterparts. The parties may sign multiple counterparts of this Supplemental Indenture. Each signed counterpart shall be deemed an original, but all of them together represent one and the same agreement.

7. Headings. The headings of this Supplemental Indenture have been inserted for convenience of reference only, are not to be considered a part hereof, and shall in no way modify or restrict any of the terms or provisions hereof.

IN WITNESS WHEREOF, the parties hereto have caused this Supplemental Indenture to be duly executed as of the date and year first above written.

| NEW GUARANTOR:
| ATLANTIC OKLAHOMA WIND, LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President

[Signature Page to Third Supplemental Indenture]

| ATLANTIC POWER CORPORATION
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President and Chief Executive Officer
| By: | /s/ Paul H. Rapisarda
|  | Name: | Paul H. Rapisarda
|  | Title: | Managing Director of Acquisitions and
|  | Asset Management
| EXISTING GUARANTORS:
| ATLANTIC AUBURNDALE, LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| ATLANTIC CADILLAC HOLDINGS, LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| ATLANTIC IDAHO WIND C, LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| ATLANTIC IDAHO WIND HOLDINGS, LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President

[Signature Page to Third Supplemental Indenture]

| ATLANTIC PIEDMONT HOLDINGS, LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| ATLANTIC POWER GENERATION, INC.
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| ATLANTIC POWER HOLDINGS, INC.
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| ATLANTIC POWER SERVICES, LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| ATLANTIC POWER SERVICES CANADA GP
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President

[Signature Page to Third Supplemental Indenture]

| ATLANTIC POWER SERVICES CANADA LP
| By: ATLANTIC POWER SERVICES CANADA GP, INC., ITS GENERAL PARTNER
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| ATLANTIC POWER TRANSMISSION, INC.
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| ATLANTIC RENEWABLES HOLDINGS, LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| AUBURNDALE GP, LLC
| By: AUBURNDALE LP, LLC,
| ITS SOLE MEMBER
| By: ATLANTIC AUBURNDALE, LLC,
| ITS SOLE MEMBER
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President

[Signature Page to Third Supplemental Indenture]

| AUBURNDALE LP, LLC
| By: ATLANTIC AUBURNDALE, LLC,
| ITS SOLE MEMBER
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| BADGER POWER ASSOCIATES, L.P.
| By: TETON POWER FUNDING, LLC,
| ITS GENERAL PARTNER
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| By: BADGER POWER GENERATION I LLC,
| ITS GENERAL PARTNER
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| BADGER POWER GENERATION I LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| BADGER POWER GENERATION II LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President

[Signature Page to Third Supplemental Indenture]

| BAKER LAKE HYDRO LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| DADE INVESTMENT, L.P.
| By: NCP DADE POWER, LLC,
| ITS GENERAL PARTNER
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| EPSILON POWER FUNDING, LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| HARBOR CAPITAL HOLDINGS, LLC
| By: ATLANTIC POWER HOLDINGS, INC.,
| ITS SOLE MEMBER
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| LAKE COGEN LTD.
| By: NCP LAKE POWER LLC
| ITS GENERAL PARTNER
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President

[Signature Page to Third Supplemental Indenture]

| LAKE INVESTMENT, L.P.
| By: NCP LAKE POWER, LLC
| ITS GENERAL PARTNER
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| NCP DADE POWER LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| NCP GEM LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| NCP LAKE POWER LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| NCP PASCO LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President

[Signature Page to Third Supplemental Indenture]

| OLYMPIA HYDRO LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| ORLANDO POWER GENERATION I LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| ORLANDO POWER GENERATION II LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| PASCO COGEN, LTD.
| By: NCP DADE POWER LLC,
| ITS GENERAL PARTNER
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| TETON EAST COAST GENERATION LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President

[Signature Page to Third Supplemental Indenture]

| TETON NEW LAKE, LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| TETON OPERATING SERVICES, LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| TETON POWER FUNDING, LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| TETON SELKIRK LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| CAPITAL POWER INCOME L.P.
| By: CPI INCOME SERVICES LTD., ITS GENERAL PARTNER
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | Chief Executive Officer

[Signature Page to Third Supplemental Indenture]

| CPI INCOME SERVICES LTD.
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | Chief Executive Officer
| CPI POWER (US) GP
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | Chief Executive Officer
| CURTIS PALMER LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President

[Signature Page to Third Supplemental Indenture]

| WILMINGTON TRUST, NATIONAL ASSOCIATION, as Trustee
| By: | /s/ Joseph P. O’Donnell
|  | Name: Joseph P. O’Donnell
|  | Title: Vice President

[Signature Page to Third Supplemental Indenture]