The Santee River is a river in South Carolina in the United States, 143 miles (230 km) long. The Santee and its tributaries provide the principal drainage and navigation for the central coastal plain of South Carolina, emptying into the Atlantic Ocean approximately 440 miles (708 km) from its farthest headwater on the Catawba River in North Carolina, Much of upper river is impounded as the expansive horn-shaped Lake Marion reservoir, formed by the 8-mile (13 km) long Santee Dam, built during the 1930s as a WPA project to provide a major source of hydroelectric power for the state.