Rio Negro (Amazon)

The Rio Negro is a river which flows through the Amazon rainforest in north-western Brazil, in the state of Amazonas.
It is the largest blackwater river in the world. It is called "Negro" (Spanish and Portuguese for "black") because its waters are colored by particles of humus, which make them look much like tea.
The Rio Negro is the largest tributary of the Amazon on the left-hand side (as it goes towards the sea). It starts in Colombia and ends in the Amazon basin.
Rio Negro has a very high species richness. About 700 fish species have been documented in the river basin, and it is estimated that the total is 800–900 fish species, including almost 100 endemics and several undescribed species. Among these are many that are important in the aquarium trade, including the cardinal tetra.