Everything that happens on the land in a watershed affects the water body into which it drains. A stream, pond or wetland can only be as healthy as its watershed. How we use the land affects the health of our aquatic resources, and in turn affects us and what we do in the watershed. In a healthy watershed, water is filtered and stored, but as water runs downhill, it can pick up whatever is on the ground beginning a process of altering water quality. When it flows through cities or across fields and pastures, water picks up dirt, pollutants, and heat. These contaminants flow into a stream, wetland or lake, affecting the water you use to drink, swim, or fish.