Oahe, Lake

Lake in South Dakota, USA, formed by the Oahe Dam (completed 1963), on the Missouri River, just northwest of Pierre. Part of the Missouri River Basin Project, the dam is one of the world's largest earthfill structures, 2,860 m/9,400 ft long and 74 m/242 ft high.

The lake backs up on the Missouri for about 400 km/250 mi, to just below Bismarck, North Dakota. To the west it extends up the Cheyenne River, a tributary, and forms the southern boundary of the Cheyenne River Indian Reservation. Mobridge, South Dakota, and the Standing Rock Reservation also lie on the Missouri section.