Pacific Northwest Pumped Storage Hydropower Development Act of 2021 This bill provides the Department of the Interior exclusive authority to develop hydropower facilities in certain instances and contains other related provisions. Specifically, Interior shall have exclusive authority to develop small conduit hydropower using Bureau of Reclamation facilities and pumped storage hydropower that exclusively use bureau reservoirs. Currently, the Federal Energy Regulatory Commission (FERC) also has regulatory authority over some of the bureau infrastructure involved in such projects, so some projects require approval from both Interior and FERC. The bill also imposes various requirements related to certain proposed projects involving specified tribes in Washington State. Before Interior may issue a lease to use power generated from such a project, the parties involved must agree to a study plan that lays out certain information, time lines, and procedures for addressing issues. Such a lease must also meet certain requirements, such as conditions to ensure that the project will not interfere with the tribes' hunting and fishing rights.