Amazonas

Brazil

Reflection of the cloud on a black water tributary river of the Amazon.
Reflection of the cloud on a black water tributary river of the Amazon.
Sunset after departing parrot cove on the Amazon River
In Manaus, Brazil, the Amazon River and the Rio Negro merge. The Amazon is the sandy colored water, and the Rio Negro is the dark colored water. For almost 4 miles the two rivers run side by side without mixing. It's one of those things you almost have to see to believe. I saw it with my own two blue eyes, so I do believe!!
The Meeting of Waters (Portuguese: Encontro das Águas) is the confluence between the Rio Negro, a river with dark (almost black colored) water, and the sandy-colored Amazon River or Rio Solimões, as it is known the upper section of the Amazon in Brazil. For 6 km (3.7 mi) the river's waters run side by side without mixing. It is one of the main tourist attractions of Manaus, Brazil. 

This phenomenon is due to the differences in temperature, speed and water density of the two rivers. The Rio Negro flows at near 2 km per hour at a temperature of 28°C, while the Rio Solimões flows between 4 to 6 km per hour at a temperature of 22°C. [1]