Blackfeet Water Rights Settlement Act of 2011

Blackfeet Water Rights Settlement Act of 2011 - Directs the Secretary of the Interior, in providing to the Blackfeet Tribe of the Blackfeet Indian Reservation of Montana the St. Mary River water right, to allocate to the Tribe 50,000 acre-feet per year of stored water in Lake Sherburne Reservoir as part of the tribal water right. Exempts the Tribe from any requirement to pay any costs associated with the allocation. Prohibits the allocation from being increased by any year-to-year carryover storage.

Requires the Tribe and the Secretary to enter into an agreement to lease the water allocated to the Tribe for use by the Secretary for the Milk River Project.

Requires, as part of the tribal water right, the Secretary to allocate permanently to the Tribe all remaining unallocated water in Lake Elwell. Exempts the Tribe from any requirement to pay any costs associated with the allocation. Prohibits the allocation from being increased by any year-to-year carryover storage.

Directs the Secretary to carry out activities necessary to: (1) planning, design, and construction for rehabilitation and improvement of the Blackfeet Irrigation Project; (2) the completion to authorized acreage of the Blackfeet Irrigation Project; and (3) planning, design, and construction for rehabilitation and improvement of the Four Horns Dam and Reservoir and associated delivery systems of the Blackfeet Irrigation Project.

Authorizes, ratifies, and confirms a specified compact and the Birch Creek Agreement.

Holds the tribal water right in trust by the United States for the benefit of the Tribe.

Establishes: (1) the Blackfeet Land and Water Development Fund, and (2) the Birch Creek Mitigation Fund.

Sets forth requirements concerning: (1) water rights in the Lewis and Clark National Forest, and (2) Milk River water rights.