Savannah River
Most of the southern half of McDuffie County, south of Thomson, is located in the Brier Creek sub-basin of the Savannah River basin, except for a slice of the eastern portion of the county, north of Dearing and along a north–south line running through Boneville, which is located in the Middle Savannah River sub-basin of the Savannah River basin. The northern half of McDuffie County, north of Thomson, is located in the Little River sub-basin of the same Savannah River basin.