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
Norris Dam State Park the Norris Project in the 1930s, is located a few miles south of the dam. Norris Dam State Park is located entirely within the Appalachian Ridge-and-Valley Range, which is characterized by narrow elongated ridges flanked by broad, fertile river valleys. The low rolling hills that dominate the park's terrain are underlain by sedimentary rocks— namely limestone, dolomite, shale, and sandstone— which were formed roughly 400-500 million years ago during the Paleozoic Era. Most of Norris Dam State Park is coated by an Appalachian oak-pine forest, much of which is second-growth, although significant old growth stands remain in nearby Chuck Swan