This and the next 3 pictures are example of the "confluenc" at the Amazon River.
The Amazon system actually comprises two different types of rivers: brown rivers and clear rivers. The brown streams, like the Amazon proper, about the color of coffee with cream, flow over sedimentary rocks and carry huge loads of suspended sediments. The blacke river waters flow over crystalline rock fomations and drain heavily forested areas. They are either clear or or have the tinge of strong undiluted tea or cola. A color derived from tannins leached from dead vegetation. The two river waters differ in temperature and thus density and acidity and resist mixing. Thus when a brown and black rivers meet, the waters flow side by side for many miles downstream before eventually mixing. The two best places to observe this phenomenon is in Manaus and Santarem, usually described as the "confluence" or "the mixing of the waters.