Lake Oahe Lake Oahe 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 and a maximum depth of . By volume, it is the fourth-largest reservoir in the US. Lake Oahe has a length of approximately and has a shoreline of . 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. Lake Oahe begins just north of
Rock Island Dam Rock Island Dam Rock Island Dam is a hydroelectric dam on the Columbia River in the U.S. state of Washington. Chelan County Public Utility District's "Rock Island Dam and Hydro Project" was the first dam to span the Columbia, having been built from 1929 to 1933. It is located near the geographical center of Washington, about 12 miles (19 km) downstream from the city of Wenatchee. By river, the dam is 235 miles (378 km) south of the Canada–US border and 453 miles (729 km) above the mouth of the river at Astoria, Oregon. The dam's reservoir is called Rock