Negro River, river, southern Argentina, whose major headstreams, the Neuquén and the Limay, rise in the Andes Mountains near the Chilean border. At Neuquén 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), or 700 miles (1,125 km) including the Neuquén, 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.