Reclamation (Reclamation) administers the Klamath Irrigation Project, which uses water from the Klamath River Basin to irrigate parts of Oregon and California. After the Department began developing the Klamath Project Operation Plan (Plan) to provide water allocations among competing uses and users, the Department asked the Klamath and other Indian tribes (Basin Tribes) to consult with Reclamation on the matter. A memorandum of understanding between those parties called for assessment, in consultation with the Basin Tribes, of the impacts of the Plan on tribal trust resources. During roughly the same period, the Department’s Bureau of Indian Affairs (Bureau) filed claims on behalf of the Klamath Tribe in an Oregon state court proceeding intended to allocate water rights. Because the Bureau is responsible for administering land and water held in trust for Indian tribes, it consulted with the Klamath Tribe. The Bureau and the Klamath Tribe then exchanged written memos on the appropriate scope of the claims ultimately submitted by the government for the benefit of the Tribe.

The Klamath Water Users Protective Association (Association) is a nonprofit organization, most of whose members receive water from the Klamath Irrigation Project. Because of the scarcity of water, most Association members have interests adverse to the tribal interests. The Association filed a series of requests with the Bureau under the Freedom of Information Act (FOIA), seeking access to communications between the Bureau and the Basin Tribes. In response, the Bureau turned over several documents but withheld others on the basis of FOIA Exemption 5. That exemption protects from disclosure “inter-agency or intra-agency memorandums or letters which would not be available by law to a party other than an agency in litigation with the agency.” Arguing that Exemption 5 did not apply, the Association sued the Bureau and the Department under FOIA to compel release of the documents. Did Exemption 5 apply?