Winters v. United States

The Gros Ventre and Assiniboine Tribes ceded most of their land to the United States in 1888 in exchange for the arid Fort Belknap Reservation, bordered by rivers essential for irrigation; the cession agreement said nothing explicitly about water rights. Winters (defendant) later settled nearby land bordering the same waterways, unaware of any tribal water claims. After Montana became a state, the United States sued on the Tribes' behalf to establish their water rights against Winters, who argued his land was equally worthless without water access and that any tribal water rights were extinguished when Montana joined the Union under the equal-footing doctrine.

Whether, if water is necessary to the full use of reservation lands, Indians will be presumed to have rights over that water.