SIXTH SUPPLEMENTAL INDENTURE

Exhibit 4.16

SIXTH SUPPLEMENTAL INDENTURE

THIS SIXTH SUPPLEMENTAL INDENTURE (this “Supplemental Indenture”), dated as of January 29, 2013, by and among each of the entities set forth on Schedule 1 attached hereto (each, a “New Guarantor” and, collectively, the “New Guarantors”), Atlantic Power Corporation, 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”).

WITNESSETH:

WHEREAS, Atlantic Power has heretofore executed and delivered to the Trustee an Indenture (together with any amendment, supplement or modification thereto, the “Indenture”), dated as of November 4, 2011, providing for the issuance of its 9% Senior Notes due 2018, Series A (the “Series A Notes”) and its 9% Senior Notes, due 2018, Series B, (the “Series B Notes” and, together with the Series A Notes, the “Notes”);

WHEREAS, Atlantic Ridgeline Holdings, LLC, a Delaware limited liability company and a wholly-owned indirect subsidiary of Atlantic Power, has acquired the New Guarantors;

WHEREAS, under certain circumstances Atlantic Power is required (or permitted) to cause the New Guarantors to execute and deliver to the Trustee a supplemental indenture pursuant to which each 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 Guarantors, 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. Each 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, each 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.

[Signature Pages Follow]

2

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

Signature Page to Sixth Supplemental Indenture

Signature Page to Sixth Supplemental Indenture

Signature Page to Sixth Supplemental Indenture

Signature Page to Sixth Supplemental Indenture

Schedule 1

New Guarantors