NEGRO RIVER

Spanish Ro Negro, Portuguese Rio Negro, river in Uruguay, rising in the southern highlands of Brazil just east of Bag. The Negro flows southwestward into Uruguay, where it is dammed near Paso de los Toros to create the Rincn del Bonete Reservoir (also called the Gabriel Terra Reservoir, or the Rio Negro Reservoir), the largest artificial lake in South America (4,000 square miles [10,360 square km]). Downstream are two dams, the Baygorria (Rincn de Baygorria) and Palmar, which are a major source of hydroelectric power for Uruguay. Below the dams the river meanders westward past Mercedes to join the Uruguay River at Soriano. The confluence is marked by several islands, the largest of which are Vizcano, Lobos, and Infante. Although the Negro is approximately 500 miles (800 km) long, it is navigable for only 45 miles (72 km) upstream from its mouth. Canoe on the Negro River in the Amazon rainforest, Amazonas state, northern Brazil. Portuguese Rio Negro, Spanish Ro Negro, major tributary of the Amazon. It originates in several headstreams, including the Vaups (Maps) and the Guaina, which rise in the rain forest of eastern Colombia. The Guaina flows east and then arches northeast and southeast, forming the ColombianVenezuelan border. Below its junction near San Carlos de Ro Negro with the Brazo Casiquiare, a natural waterway that brings water from the Orinoco River in Venezuela, the river acquires the name Negro and enters Brazil. The Negro meanders generally east-southeastward, picking up the Branco River (q.v.) and other tributaries, to Manaus. There it joins the Solimes River (q.v.) to form the Amazon. Its length is about 1,400 mi (2,253 km), of which 850 mi are in Brazil. It is navigable for about 450 mi above its mouth. Although settlement along its banks is sparse, the river is a major transportation artery. The clear, jet-black colour of the Negro's water, whence comes its name, is caused by the decomposition of organic matter in marginal swamps and its low silt content; its colour contrasts dramatically with the yellowish, silt-laden waters of the Branco and with the Amazon. Spanish Ro Negro, river, southern Argentina, whose major headstreams, the Neuqun and the Limay, rise in the Andes Mountains near the Chilean border. At Neuqun city they meet to form the Negro, which flows generally east-southeastward across northern Patagonia and empties into the Atlantic Ocean southeast of Viedma and Carmen de Patagones. The length of the Negro is about 400 miles (640 km; 700 miles [1,125 km], including the Neuqun), but only the lower 250 miles (400 km) are navigable. The waters of the Negro are used for hydroelectricity and for irrigation of grains and fruit, including wine grapes and apples for export to Europe.