A
blackwater river is a type of a river with a deep, slow-moving channel flowing through forested
swamps or
wetlands. As vegetation decays,
tannins leach into the water, making a transparent, acidic water that is darkly stained, resembling tea or black coffee. 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.