The Waccamaw River is a river, approximately 140 miles (225 km) long, in southeastern North Carolina and eastern South Carolina in the United States. It drains an area of approximately 1,110 square miles (2886 km2) in the coastal plain along the eastern border between the two states into the Atlantic Ocean. Along its upper course, it is a slow-moving, blackwater river surrounded by vast wetlands, passable only by shallow-draft watercraft such as canoe. Along its lower course, it is lined by sandy banks and old plantation houses, providing an important navigation channel with a unique geography, flowing roughly parallel to the coast.

A blackwater river is a type of river with a slow-moving channel flowing through forested swamps or wetlands. Most major blackwater rivers are in the Amazon Basin and the Southern United States. The term is used in fluvial studies, geology, geography, ecology, and biology. Not all dark rivers are blackwater in that technical sense. Some rivers in temperate regions, which drain or flow through areas of dark black loam, are simply black due to the color of the soil; these rivers are black mud rivers. There are also black mud estuaries.