Savannah River
The southern three-quarters of Columbia County is located in the Middle Savannah River sub-basin of the Savannah River basin. A very small corner in the northeast of the county, west of Clarks Hill, is located in the Upper Savannah River sub-basin of the larger Savannah River basin. The northern portion of Columbia County, north of Appling, is located in the Little River sub-basin of the same Savannah River basin, while the southwestern corner of the county, south of Harlem, is located in the Brier Creek sub-basin of the Savannah River basin.