Look at a map of the Amazon, and you'll see that it is not one river but more than a thousand. Somewhere around 1,100 tributaries flow into the Amazon to create the world's largest river. Just downstream from Manaus, the place where two of these tributaries meet is one of the area's principal attractions. The water of the Rio Solimões is lighter colored and rich with sediment from the Andes, while the Rio Negro is, as its name implies, darker. Due to the different speeds and temperatures of the rivers, they flow side-by-side but still separate for some six kilometers (four miles) until they reach a set of rapids, emerging on the other side as one river, the Lower Amazon.