The Blackwater River of southeastern Virginia flows from its source near the city of Petersburg, Virginia for about 105 miles (170 km) through the Inner Coastal Plain region of Virginia. The Blackwater joins the Nottoway River to form the Chowan River, which empties into Albemarle Sound. The Blackwater-Nottoway confluence forms the boundary between Virginia and North Carolina.

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.