The Negro (Spanish: black) River, the great northern tributary of the Amazon River and the largest blackwater river in the world, has its sources along the watershed between the Orinoco and the Amazon basins, and also connects with the Orinoco by way of the Casiquiare canal. Its main affluent is the Vaupés River, which disputes with the headwaters of the Guaviare branch of the Orinoco River the drainage of the eastern slope of the "Oriental", Andes of Colombia.

The Amazon and Negro rivers join near Manaus. The muddy Amazon is laden with silt carried down from the Andes; the darker Negro has its source in a region with little sediment

The Negro is navigable for 450 miles above its mouth for 4 feet of water in the dry season, but it has many sandbanks and minor difficulties. In the wet season, it overflows the country far and wide, sometimes to a breadth of 20 miles, for long distances, and for 400 miles up, as far as Santa Isabella, is a succession of lagoons, full of long islands and intricate channels, and the slope of the country is so gentle that the river has almost no current. But just before reaching the Vaupés, there is a long series of reefs, over which it violently flows in cataracts, rapids and whirlpools. The Uaupes is full of similar obstacles, some fifty rapids barring its navigation, although a long stretch of its upper course is said to be free from them, and to flow gently through a forested country. Despite the impediments, canoes ascend this stream to the Andes.

"Black River", as the name of the river means in Spanish, is a misnomer; though dark, the water is actually a similar colour to clear tea.

There is another river called Río Negro in Argentina.