The term watershed describes an area of land that drains downhill to the lowest point.
- The water starts at the highest area on the terrain (headwaters), flowing downhill moving through a network of drainage pathways. It is relatively easy to delineate watersheds using a topographic map that shows stream channels. Watershed boundaries follow major ridge lines around channels and meet at the bottom, where water flows out of the watershed, a point commonly referred to as a stream or river.
- The rain water flows creating small streams called tributaries, and grows progressively larger as the water moves on downstream, filling streams and rivers and eventually reaching lakes, reservoirs, and eventually the ocean. In Tennessee, streams flow into larger basins and then into the Mississippi River, which then drains into the ocean at the Gulf of Mexico.
- Other terms used interchangeably with watershed include drainage basin and catchment basin. Watersheds can be large or small. Every stream, tributary, or river has an associated watershed, and small watersheds join to become larger watersheds. For example, the Stones River is one of 14 watersheds that make up the Cumberland River Basin.
- Water can travel both underground (groundwater) and on the surface (surface water). These are connected. Rain flows into sinkholes and karst windows, flowing as groundwater below the surface eventually coming out at a spring.
- Rain also picks up pollutants as it washes through the community and landscape. Pollutants include fertilizers, pesticides, animal waste, septic leaks, automobile fluids, brake dust, and many others. As citizens, we can do a lot to prevent pollution through easy daily actions to protect water quality.