Rio Negro (Amazon)

For other uses, see Rio Negro (disambiguation).

Río Negro
Guainía River
300px Sunset over the Rio Negro, upstream from Manaus
Countries	Brazil, Colombia, Venezuela
Tributaries
- left	Branco River (and many smaller rivers)
- right	Vaupés River (and many smaller rivers)
Source	highlands of Colombia
- location	Guainía Department, Amazon region, Colombia
Mouth	Amazon River
- location	Manaus, Amazonas State, Brazil
- coordinates
Length	2,250 km (1,400 mi)
Basin	691,000 km2 (267,000 sq mi)
Discharge	mouth
- average	28,000 m3/s (988,800 cu ft/s)
Map showing the Rio Negro in the Amazon Basin

The Rio Negro (Portuguese: Rio Negro [ˈʁi.u nɛɡɾu]; Spanish: Río Negro [ˈri.o ˈneɣɾo] "Black River") is the largest left tributary of the Amazon, the largest blackwater river in the world, and one of the world's ten largest rivers in average discharge. It has its sources along the watershed between the Orinoco and the Amazon basins, and also connects with the Orinoco by way of the Casiquiare canal in southern Venezuela. In Colombia, where the Rio Negro's sources are located, it is called the Guainía River. Its main affluent is the Vaupés, with sources near the headwaters of the Guaviare branch of the Orinoco, the drainage of the eastern slope of the Andes of Colombia. The Rio Negro joins with the Rio Solimões to form the Amazon River south of Manaus, Brazil.

Rio Negro is navigable for 700 kilometres (430 mi) from its mouth in 1 metre of water in the dry season, but it has many sandbanks and minor difficulties. A small portion of it forms the international boundary between Colombia and Venezuela.

In the wet season, it floods the country far and wide, sometimes to a width of 30 kilometres (19 mi), for long distances, and for 650 kilometres (400 mi) upstream. During this time, from April until October, it is a succession of lagoons, full of long islands and intricate channels as far as Santa Isabel do Rio Negro. The foothills of the Andes begin just before reaching the Vaupés River. At this point, the Negro narrows and is filled with many large rocks over which it violently flows in cataracts, rapids and whirlpools. Despite the impediments, canoes and motor launches ascend past São Gabriel da Cachoeira to the Andes.

The mouth of the Rio Negro at the "Meeting of Waters": the dark Rio Negro meeting the silty Amazon River.

While the name Rio Negro means Black River, its waters are similar in color to strong tea. The dark color comes from humic acid due to an incomplete breakdown of phenol-containing vegetation from sandy clearings. The river was named because it looks black from a distance.

Much has been written on the productivity of the Rio Negro and other blackwater rivers. The older idea that these are "hunger rivers" is giving way, with new research, to the recognition that the Rio Negro, for example, supports a large fishing industry and has numerous turtle beaches. If explorers did not find many Indians along the Rio Negro during the 17th century, it is likely that their populations were reduced because of new infectious diseases and warfare rather than low river productivity.

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.

References

• Goulding, M., Carvalho, M. L., & Ferreira, E. J. G. (1988). Rio Negro, Rich Life in Poor Water : Amazonian Diversity and Foodchain Ecology as seen through Fish Communities. The Hague: SPB Academic Publishing. ISBN 90-5103-016-9
• Saint-Paul, U., Berger, U., Zuanon, J., Villacorta Correa, M. A., García, M., Fabré, N. N., et al. (2000). "Fish communities in central Amazonian white- and blackwater floodplains," Environmental Biology of Fishes, 57(3), 235-250.
• Sioli, H. (1955). "Beiträge zur regionalen Limnologie des Amazonasgebietes. III. Über einige Gewässer des oberen Rio Negro-Gebietes." Arch. Hydrobiol., 50(1), 1-32.
• Wallace, A. R. (1853). A narrative of travels on the Amazon and Rio Negro, with an account of the native tribes, and observations on the climate, geology, and natural history of the Amazon Valley. London: Reeve.
• Wright, R. (2005). História indígena e do indigenismo no Alto Rio Negro. São Paulo, Brazil: UNICAMP & Instituto Socioambiental. ISBN 85-7591-042-6.