Overhead pictures of tropical rivers reveal another curious aspect: the meandering course. A river will twist and turn, sometimes turning almost 180 degrees back on itself. The lack of slope and the clay-like soils of many tropical regions allow rivers to have virtually free rein over their direction. The volume of water flowing through tropical forests, coupled with the soils and varying water levels, can create great river cliffs over 100 feet high, even at regular water levels. These clay banks form an important part of the local ecology in parts of the Amazon. Macaws gather by the hundreds on some of these banks to ingest minerals that bind to and detoxify chemicals in the fruits they consume.
Tropical streams and creeks are even more variable than tropical rivers and can change from a virtually dry river bed to a raging torrent 30 feet deep in a matter of hours during a heavy rain. Smaller streams and creeks are often invisible by air because they flow beneath the rainforest canopy. Despite their inconspicuousness, these waterways house an astounding array of animal life. Creeks are common in the rainforest and provide an important niche for certain fish, amphibian, and insect species in addition to providing an important source of water for other forest floor dwellers.