The Oahe Dam is a large man-made dam along the Missouri River, just north of Pierre, South Dakota in the United States. It creates Lake Oahe, the 4th largest man-made reservoir in the United States, which stretches 231 miles (372 km) up the course of the Missouri to Bismarck, North Dakota. The dam's powerplant provides electricity for much of the north-central United States. It is named for the Oahe Indian Mission established among the Lakota Sioux in 1874. The project provides flood control, electric power, irrigation, and navigation benefits, estimated by the Corps of Engineers at $150,000,000 per year.