What is a Watershed?
A watershed is the area of land that water flows across as it moves toward a common body of water, such as a stream, river or lake.
You're sitting in one right now! All of the land around you is part of a watershed. A watershed can be very large and drain thousands of square miles to a major river, lake or the ocean. It can also be very small and drain only a few acres to a small pond. Topography, the arrangement of the physical features of an area, determines where and how water flows. Ridge tops surrounding a body of water (though more subtle here in the Midwest than say, the Rocky Mountains) determine the hydrologic boundary of a watershed.
Imagine turning an open umbrella upside down while it's raining. Rain that hits anywhere within the umbrella's surface area would drain to the bottom and collect at the center of the umbrella. This is a simplified way of visualizing how water moves across a watershed.
Because water moves downstream in a watershed, any activity on the land or in the water that affects water quality or quantity at one location can change the characteristics of the watershed at locations downstream. This means everyone who lives or works in a watershed needs to take measures to protect watershed health.