The tributaries and the Amazon River are two different colors -- the "white" water rivers, which are really muddy and look much like cocoa, the "black" water rivers, which are filled with tannin and are clear like coffee. At any point where two of these rivers join, their density is so different that they will not mix for several miles. No where is this natural event more dramatic than near Manaus, where the Solimoes and the Rio Negro merge. The Amazon River is formed at the point these two rivers join together.
Rio Negro at the " Meeting of the Waters": the dark Rio Negro meeting the silty Amazon Solimoes River.