Which river in the Amazon basin is known for its black water?

The Amazon-basin river famous for its dark, tea-colored water is the Rio Negro.

Rio Negro means “Black River” in Portuguese. Its water appears nearly black because it carries dissolved organic matter, especially tannins produced as leaves and other plant material decompose in the surrounding rainforest. The water is dark but usually clear, so its color is not simply caused by mud.

The Rio Negro is one of the Amazon River’s largest tributaries. It flows through Colombia, Venezuela, and Brazil before joining the Solimões River near Manaus. Their meeting creates the celebrated Meeting of Waters, where dark Rio Negro water runs beside the lighter, sediment-rich water of the Solimões for several kilometers before mixing.

Blackwater rivers tend to be acidic and low in nutrients compared with muddy whitewater rivers. That difference affects which fish, plants, and aquatic organisms thrive there. The Tapajós is another Amazon tributary, but Rio Negro is the canonical answer to a question specifically asking for the basin’s best-known blackwater river.