The RÃÂo Negro (, Black River) is a river in southern Brazil and central Uruguay. It rises in the southern highlands of Brazil, just east of Bagé, and flows west across the entire width of Uruguay to the Uruguay River. The course of the RÃÂo Negro across Uruguay effectively divides the south and the north of the country. The RÃÂo Negro's principal tributaries are YàRiver and Tacuarembó River.
The river is dammed near Paso de los Toros, creating the Rincón del Bonete Reservoir, also called the Gabriel Terra Reservoir or the Rio Negro Reservoir. With a surface area of about , it is the largest reservoir in Uruguay and has an installed capacity of 160 MW.
Downstream from the Rincón del Bonete Reservoir, there are two more dams, the Baygorria Dam and the Constitución Dam at Palmar, which generate hydroelectric power for Uruguay with 108 MW and 333 MW, respectively.
The RÃÂo Negro's drainage basin size is about .
There is a delta at its confluence with the Uruguay River with two main mouths. YaguarÃÂ creek, bordered by Vizcaino and Lobos Islands, is the navigable entry to Negro River, and may change water flow direction when the Uruguay is high while the southern mouth (Spanish: Boca Falsa) is very wide but shallow.