The Coosaw River/Ashepoo River/St. Helena Sound Basin (portion of hydrologic unit 03050207) is located in Colleton, Hampton, and Beaufort Counties and encompasses 5 watersheds and 830 square miles. The Coosaw River/Ashepoo River/St. Helena Sound Basin flows through the Lower Coastal Plain and Coastal Zone regions. Of the 531,261 acres, 36.0% is forested land, 25.4% is forested wetland, 16.2% is nonforested wetland, 8.9% is agricultural land, 8.8% is water, 4.4% is urbanland. and 1.2% is barren land. There are approximately 1,426 stream miles, 1,331 acres of lake waters, and 38,505 acres of estuarine areas in this basin.
The Combahee River is formed from the confluence of the Salkehatchie and Little Salkehatchie River and flows into the Coosaw River. The Coosaw River joins the Ashepoo River and the Morgan River to form St. Helena Sound. The Ashepoo River originates near the City of Walterboro and accepts drainage from the Great Swamp and Horseshoe Creek before flowing into St. Helena Sound.
For an overview of water quality in the Coosaw River/Ashepoo River/St. Helena Sound Watershed, download the water quality assessment summary. For specific basin descriptions, facts, figures, and detailed maps click on a watershed below.