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What is a watershed?

A watershed is the area of land that catches precipitation (like rain and snow) and drains or seeps into a marsh, stream, river, lake, ocean or groundwater.

In much of Dane County, Wisconsin, precipitation running off the land surface is carried to the Yahara River, which flows to the Rock River, then the Mississippi River. Where does the Mississippi flow?

Watersheds can be as big as all the land that drains into the Pacific Ocean, or as small as an acre that drains into your schoolyard pond. Madison, Wisconsin is part of many different watersheds, one bigger than the next. The Yahara Watershed is part of the larger Rock River Watershed, which is in turn part of the Mississippi River Watershed.

Watersheds are made up of houses, neighborhoods, schools, farms, parks, big cities, and little towns. A watershed doesn't always pay attention to human-made borders, either. Some cross city, county, state, and even international borders.

One way of looking at a watershed is through a watershed wheel. This is a way to show how the interaction of space and time serves to organize the variety of life and activities in the watershed on an annual basis.

Why watersheds?

The watershed provides a powerful study and management unit which integrates ecological, geographical, geological, and cultural aspects of the land. The watershed is also a useful concept for integrating science with historical, cultural, economic, and political issues. Water (movement, cycling, use, quality, etc.) provides a focus for integrating various aspects of watershed use and for making regional and global connections.

Using the watershed concept, one can start with study of any number of small sub systems (e.g., a particular marsh or sub-watershed; or a particular pollutant, such as salt), and continually relate these small-scale issues to questions of larger-scale watershed system health.

Why watershed protection?

A Watershed Protection Approach is a strategy for effectively protecting and restoring aquatic ecosystems and protecting human health. This strategy has as its premise that many water quality and ecosystem problems are best solved at the watershed level rather than at the individual water body or discharge level. Major features of a Watershed Protection Approach are targeting priority problems, promoting a high level of stakeholder involvement, integrated solutions that make use of the expertise and authority of multiple agencies, and measuring success through monitoring and other data gathering.

—from EPA's Introduction to The Watershed Approach