A river is characterized by continuously flowing water from an upland source into lakes, wetlands or the sea. Rivers are fed by tributary streams or springs, and they include a river channel, shoreline and a floodplain.
All rivers have a river bed, which all differ from one another. Some rivers have beds filled with boulders and gravel, while others have beds that are either sandy and flat or muddy and full of weeds. River beds provide an essential habitat for the fish and animals that reside in the rivers. Alongside every river is a shoreline, and somewhere along the shoreline, there is a floodplain. A floodplain is the area where the river ends up when it has more water than it can hold in its channel. Floodplains are broad, flat areas that play an important role when it comes to nutrient cycling within a river, according to The Encycolpedia of Earth.
Some rivers have dams, which are built to control flood waters and/or produce hydroelectric power. A reservoir will hold the waters from a flood away from the dam until those waters can be slowly released. The water is released when the flow of the river is low, according to The Encyclopedia of Earth.