With respect to water systems, we often talk about watersheds. Watersheds catch, store, and release water. When rain falls or snow melts, the water flows downhill, collecting into wetlands, small streams, and drainages, which then feed streams, rivers, lakes, and recharge groundwater. In Michigan, these waters then flow into or connect to one of the Great Lakes. The land area that collects the water that feeds a body of water is called a watershed.
As water flows across land, it gathers sediments, debris, and dissolved substances. Along the way, physical, chemical, and biological processes also affect the amount and quality of the water. As a result, water quality at any point in the watershed may have a significant impact on the water quality of the entire watershed.
The health of the watershed and its ability to function properly is a direct reflection of the health of the land area within the watershed. Healthy watersheds recharge aquifers and release high quality water into larger bodies of water. Healthy watersheds create good habitat for aquatic species. Healthy watersheds are resilient to floods, fire, and drought, and they are capable of ameliorating the impacts of some human activity. Healthy watersheds provide clean, safe drinking water. Because healthy watersheds are essential to maintaining and protecting water quality, both the state and federal government agencies involved in water quality permitting emphasize watershed management.
-A Citizen's Guide to Water Quality Permitting, EGLE, 2005