A watershed, also known as a drainage basin, is an area of land where surface water from rain and snow collects, flows downhill through water channels, and eventually exits and ends into a body of water. In a closed watershed, water drains to a point within the watershed such as a permanent or dry lake. Otherwise, the water drains to a body of water outside of the watershed such as a lake, river, wetland, ocean, or estuary. A watershed is made up by the streams and rivers by which the water is channeled, and the land area from which the water was collected.
A watershed can also be conceptualized as a sink. Water that falls into a sink flows downward toward the drain. Likewise, rain or snow that enters into the watershed flows downward through rivers and streams, and is drained out. Watersheds are made up of many streams and rivers which lead to the drain or end point (a body of water).
An example of a watershed can be our very own street in our neighborhood. When it rains, rain water washes trash, toxins and pollutants off our street, drains into the sewer and eventually goes into the ocean.
If individuals take care to not litter and industries and agriculture reduce the amount of pollutants they release into the environment, we can reduce the amount of waste entering into the ocean. For these same reasons we must also be careful to not release pollutants into other watersheds such as lakes, streams, and rivers because they too will drain into the ocean.
You can explore more about watersheds at Earthlabs
Thanks to Lane Council of Governments for the picture!