The Savannah River is a major river in the southeastern United States. It makes up most of the border between the states of South Carolina and Georgia. The Savannah River drainage basin extends into the southeastern side of the Appalachian Mountains just inside North Carolina. It is bounded by the Eastern Continental Divide. It is formed by the confluence of the Tugaloo River and the Seneca River. Today this confluence is under Lake Hartwell, a man-made reservoir. From Lake Hartwell to the Atlantic Ocean the Savannah River is 313 miles (504 km) long.