Whether federal agency regulatory action under the Endangered Species Act can constitute the adjudication and administration of water rights for tribal purposes, against the legal backdrop of Congress's and this Court's recognition of the primacy of state law to determine, quantify, and administer water rights

QUESTION PRESENTED Petitioners are a plaintiff class of Oregon and California farmers and ranchers who depend on their water rights in the Klamath River basin to irrigate their land. When the U.S. Bureau of Reclamation cut off their water supplies to protect endangered fish, petitioners sued the United States alleging a Fifth Amendment physical taking. Congress and this Court have determined that federal entities must defer to state water law for a comprehensive approach to quantify and administer water rights. By contrast, the Federal Circuit held that the Bureau did not take petitioners’ property interests in their water rights because state law did not apply. Instead, and in the absence of any state adjudicatory determination of water rights, the Federal Circuit concluded that there exist senior tribal water rights to quantities of water at least as great as the water the Bureau determined was required for fish under the Endangered Species Act. Petitioners and the State of Oregon explained below that this decision upends a century of western water law and destroys the efficacy of Oregon’s adjudication of state-based and federal reserved water rights, which Congress endorsed in the McCarran Amendment, 43 U.S.C. 666, and Reclamation Act, 43 U.S.C. 372, 383. The question presented is: Whether, against the legal backdrop of Congress’s and this Court’s recognition of the primacy of state law to determine, quantify, and administer water rights, a federal court may deem federal agency regulatory action under the Endangered Species Act to constitute the adjudication and administration of water rights for tribal purposes.