From its source to its mouth the Congo crosses three different regions: the Upper Congo, which consists of numerous streams, waterfalls, lakes and rapids; the Middle Congo, which drops through seven great cataracts (the Stanley Falls or Ngaliema); and the Lower Congo, which divides to form a huge pool, the Stanley (Malebo) Pool. The flow of the river is regular since it is fed throughout the year by waters from tributaries arising on either side of the equator; this means in effect that it has no dry season. Much of the Congo Basin is covered by dense evergreen equatorial rainforest, bordered by belts of savanna. The river is rich in fish of many species as well as crocodiles.