What is a River System?

Every river is part of a larger system—a watershed, which is the land drained by a river and its tributaries. Rivers are large natural streams of water flowing in channels and emptying into larger bodies of water. This diagram shows some common characteristics of a river system. Every river is different, however, so not all rivers may look exactly like this illustration.



The river source, also called the headwaters, is the beginning of a river. Often located in mountains, the source may be fed by an underground spring, or by runoff from rain, snow-melt, or glacial melt.

A tributary is a smaller stream or river that joins a larger or main river.

The main river is the primary channel and course of a river.

A fully-developed floodplain is relatively flat land stretching from either side of a river, which may flood during heavy rain or snow-melt. Built of materials deposited by a river, floodplain soil is often rich in nutrients and ideal for growing food.

meander is a loop in a river channel. A meandering river winds back and forth, rather than following a straight course.

Upstream is in the direction of or nearer to the source of a river

Wetlands are low-lying areas saturated with water for long enough periods to support vegetation adapted to wet conditions. Wetlands help maintain river quality by filtering out pollutants and sediments, and regulating nutrient flow.

The river mouth is the place where a river flows into a larger body of water, such as another river, a lake, or an ocean.

watershed boundary, also called a drainage divide, marks the outer-most limit of a watershed. A watershed is a tract of land drained by a river and its tributaries. Anything that affects a watershed may eventually impact its tributaries and river as well as the water body at the mouth of the river. People’s actions within a watershed can affect the overall quality of its rivers.

Downstream is in the direction for or nearer to the mouth of a river. All rivers form part of the water cycle.