The point where a river begins is referred to as its "headwaters," which is usually the smallest part of the entire river. Headwaters can start out in marshy areas or where there are natural underground springs. The beginning of a river can also be fed from thousands of small streams that flow in the same direction.
Water that flows out of the river's headwaters continues down the river's channel until it reaches a large body of water. Along the river's channel are river banks, which are home to many different kinds of wildlife and vegetation. Areas called "floodplains" are flat, low areas beside a river that fill up with water when the water level in a river becomes too high. Heading downstream, the water in a river will eventually reach the delta, or mouth, where it slows down and enters another body of water, such as a lake, ocean or wetland.