US Army Corps of Engineers

Surrounded by the rolling prairies of the Dakotas, Lake Oahe is the fourth largest man-made lake in the United States, stretching 230 miles from Pierre, South Dakota to Bismarck, North Dakota.

The dam consists of an earthen embankment, an outlet structure with six tunnels for releasing stored water, a powerhouse, and eight spillway gates on a concrete-lined spillway. During normal operations, USACE releases water through the powerhouse to generate power and balance reservoir levels for other uses. As operations shift to reducing flood risks during periods of high runoff, water also is released through the outlet structure and if needed, USACE dam operators can release more water through the spillway gates.