Stream channels are created as runoff from the watershed seeks a path of least resistance. If the watershed has very steep terrain, the resulting swift-moving water may cut a deep stream channel and keep the stream bed flushed of sediments. If the topography is flat, the stream may be shallow and meandering, with many sediments found suspended within the water. In its natural condition, a stream channel provides a variety of aquatic habitats for many species of plants and animals. These stable habitats provide areas for feeding, resting and reproduction, and generally support a great diversity of organisms.
Rivers are large natural streams that return excess rain or snow to the ocean.
They are extremely important as a source4s of water supply, avenues for commerce and sources of hydroelectric power. The amount of water a river will yield is the result of many factors. The size of the drainage basin is basic, because large catchment areas are necessary for large and reliable supplies. Climate is critical, for small river basins in humid areas may yield as much water as much larger basins in dry regions. Many problems besides yield must be faced in using rivers for water supply.