Here is the opinion in Navajo Nation v. Dept. of the Interior. Briefs here.

An excerpt:

Moreover, neither Morongo nor Gros Ventre nor Jicarilla involved claims to vindicate Winters rights, which provide the foundation of the Nation’s claim here. Unlike the plaintiffs in those cases, the Nation, in pointing to its reserved water rights, has identified specific treaty, statutory, and regulatory provisions that impose fiduciary obligations on Federal Appellees—namely, those provisions of the Nation’s various treaties and related statutes and executive orders that establish the Navajo Reservation and, under the long-established Winters doctrine, give rise to implied water rights to make the reservation viable.

                      *. *  *

We hold in particular that, under Winters, Federal Appellees have a duty to protect the Nation’s water supply that arises, in part, from specific provisions in the 1868 Treaty that contemplated farming by the members of the Reservation.