Everybody lives in a watershed. A watershed is all the land drained by a particular river.

All the raindrops or snowflakes that fall in a watershed eventually end up in the same river, whether they arrive there over land, by secret underground labyrinths, or via big cement pipes. (Of course, this doesn't include the raindrops that evaporate, get slurped up by a plant or animal, or remain hidden in deep natural aquifers).

The borders of watersheds are high points, such as ridgelines. Rain that falls on one side of the ridge may end up in another river than rain that falls on the other side of the ridge. In a very general sense, the overall shape of a watershed is a basin, with the river running along the bottom. A watershed is sometimes called a drainage basin or a river basin.

Watersheds come in all sizes—little ones for small creeks and enormous ones for big rivers. Each large watershed is made of up smaller watersheds that fit together like puzzle pieces.

Do you know what river drains your land?

The Mississippi River basin is the largest watershed in the United States. It drains land from Montana to New York and from New Mexico to western North Carolina, before flowing into the Gulf of Mexico in Louisiana.

Large watersheds support different kinds of natural communities than smaller ones. For example, the Mississippi River has a much wider floodplain and is capable of experiencing much larger floods than a small stream. As a result, the Mississippi’s floodplain communities are different than those of the floodplains of smaller streams.

Other factors about watersheds that affect natural communities include

  • how steep or gentle the terrain is (will the precipitation run right off, or soak in?)
  • how much precipitation falls each year (enough to support trees, or smaller plants, or just desert plants?)
  • patterns of precipitation (steady year round? infrequent flooding torrents?)
  • the proportion of precipitation that flows directly to the stream rather than soaking into the ground or evaporating (is flash flooding more or less likely?)

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