Lake Oahe (oh-WAH'-hee) is a large reservoir behind Oahe Dam on the Missouri River; it begins in central South Dakota and continues north into North Dakota in the United States. The lake has an area of 370,000 acres (1,500 km2) and a maximum depth of 205 ft (62 m). By volume, it is the fourth-largest reservoir in the US. Lake Oahe has a length of approximately 231 mi (372 km) and has a shoreline of 2,250 mi (3,620 km). 51 recreation areas are located along Lake Oahe, and 1.5 million people visit the reservoir every year. The lake is named for the 1874 Oahe Indian Mission.