Río Negro (Argentina)

Río Negro (; "Black River") is the most important river of the Argentine province of Río Negro, and Patagonia. Its name comes from the literal translation of the Mapuche term "Curu Leuvu", although the water is more green than black. 
Formerly, it was also known as "river of the willows" because of the big number of weeping willows that grow along the bank. It's 635 km in length.