Opinion of the Court
corn.
In “consideration of the advantages and benefits conferred” on the Navajos by the United States in the 1868 treaty, the Navajos pledged not to engage in further war against the United States or other Indian tribes. Id., at 669–670. The Navajos also agreed to “relinquish all right to occupy any territory outside their reservation”—with the exception of certain rights to hunt. Id., at 670. The Navajos promised to “make the reservation” their “permanent home.” Id., at 671. In short, the treaty enabled the Navajos to live on their original land. See Treaty Between the United States of America and the Navajo Tribe of Indians With a Record of the Discussions That Led to Its Signing 2, 4, 10–11, 15 (1968).
Under the 1868 treaty, the Navajo Reservation includes not only the land within the boundaries of the reservation, but also water rights. Under this Court’s longstanding reserved water rights doctrine, sometimes referred to as the Winters doctrine, the Federal Government’s reservation of land for an Indian tribe also implicitly reserves the right to use needed water from various sources—such as groundwater, rivers, streams, lakes, and springs—that arise on, border, cross, underlie, or are encompassed within the reservation. See Winters v. United States, 207 U. S. 564, 576–577 (1908); see also Cappaert v. United States, 426 U. S. 128, 138–139, 143 (1976); Arizona v. California, 373 U. S. 546, 598–600 (1963); F. Cohen, Handbook of Federal Indian Law §19.03(2)(a), pp. 1212–1213 (N. Newton ed. 2012). Under the Winters doctrine, the Federal Government reserves water only “to the extent needed to accomplish the purpose of the reservation.” Sturgeon v. Frost, 587 U. S. ___, ___ (2019) (slip op., at 13) (internal quotation marks omitted); United States v. New Mexico, 438 U. S. 696, 700–702 (1978).
The Navajo Reservation lies almost entirely within the Colorado River Basin, and three vital rivers—the Colorado,
