South Atlantic–Gulf water resource region
The South Atlantic–Gulf water resource region is one of 21 major geographic areas, or regions, in the first level of classification used by the United States Geological Survey to divide and sub-divide the United States into successively smaller hydrologic units. These geographic areas contain either the drainage area of a major river, or the combined drainage areas of a series of rivers. The South Atlantic–Gulf region, which is listed with a 2-digit hydrologic unit code (HUC) of 03, has an approximate size of , and consists of 18 subregions, which are  listed with the 4-digit HUCs 0301 through 0318. This region includes the drainage that ultimately discharges into: (a) the Atlantic Ocean within and between the states of Virginia and Florida; (b) the Gulf of Mexico within and between the states of Florida and Louisiana; and (c) the associated waters. The geographic area of the South Atlantic–Gulf region includes all of Florida and South Carolina, and parts of Alabama, Georgia, Louisiana, Mississippi, North Carolina, Tennessee, and Virginia.