Savannah River, a river in the southeastern United States, forming most of the Georgia-South Carolina boundary. From Hartwell Lake it flows southeastward for about 314 miles (505 km) to the Atlantic Ocean. Savannah and Augusta, both in Georgia, are the principal cities on the river. J. Strom Thurmond Dam, upstream from Augusta, impounds a second large reservoir. Both Hartwell and J. Strom Thurmond dams are important for flood control and the generation of hydroelectric power. The river is navigable for oceangoing vessels to Savannah and for small craft to Augusta.