Negro, Río (rēˈō nāˈgrō) [key], principal river of Uruguay, c.500 mi (800 km) long, rising in S Brazil and flowing SW across central Uruguay to the Uruguay River. It traverses a sheep-raising region; there is agriculture along its lower course. On the river is Embalse del Río Negro (c.4,000 sq mi/10,360 sq km), the largest artificial lake in South America. It extends 87 mi (140 km) upstream from Rincón del Bonete, a hydroelectric dam (completed 1949) with a 128,000-kW capacity. Downstream from Bonete is Rincón de Baygorria (1960), with a 108,000-kW capacity.