A watershed is an area of land that water flows across as it moves toward a common body of water, such as a stream, river, lake or coast. You're sitting in one now! All land is part of a watershed. A watershed can be very large, draining thousands of square miles to a major river, lake or the ocean, or very small, draining a few acres to a small pond. 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.