The Ashepoo, Combahee and Edisto Basin (abbreviated as ACE Basin, spoken as ace basin) is one of the largest undeveloped estuaries along the Atlantic Coast of the United States. Located primarily in Colleton and Beaufort counties in South Carolina, the Ashepoo, Combahee and South Edisto rivers combine into the larger St. Helena Sound and drain a significant portion of the Lowcountry region.