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The Rio Negro ( (:ˈʁi.u nɛɡɾu); (スペイン語: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 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 , for long distances, and for 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. 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.〔Hales, J., and P. Petry (2013). ''(Rio Negro )''. Freshwater Ecoregions of the World. Retrieved 12 February 2013〕 Among these are many that are important in the aquarium trade, including the cardinal tetra.〔 ==Notes== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Rio Negro (Amazon)」の詳細全文を読む スポンサード リンク
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