Bristol Bay Borough is a borough of the U.S. state of Alaska on Bristol Bay. As of the 2020 census the borough population was 843, down from 997 in 2010, the second-least populated borough in Alaska. The borough seat is Naknek. There are no incorporated settlements.

Bristol Bay is the easternmost arm of the Bering Sea, at 57° to 59° North 157° to 162° West in Southwest Alaska. Bristol Bay is 400 km (250 mi) long and 290 km (180 mi) wide at its mouth. A number of rivers flow into the bay, including the Cinder, Egegik, Igushik, Kvichak, Meshik, Nushagak, Naknek, Togiak, and Ugashik.