Here are maps of the Suwannee River Basin in the EPA EnviroAtlas, with shadings and boundaries for Hydrologic Unit Codes (HUCs). HUC-8 (eight digits) is big river basins; in this case Little, Withlacoochee, Alapaha, Santa Fe, Upper Suwannee, and Lower Suwannee. HUC-12 is more local.
What are the odd HUC-12s that are not shaded in? At least some of them, such as around Lake Octahatchee are endorheic basins. Continue reading