Think of a lake as the collection basin for all the water that is flowing downhill from the surrounding land. The land area that "drains" water to your lake is referred to as the "watershed." A watershed may be hundred or thousands of acres. The quality of our lakes is dependent on the health of their watersheds. What is a watershed?
When it rains or snow melts, water flows over (and into) the land and makes its way through gullies, streams, and groundwater into our lakes and rivers. A watershed is the area of land where all surface water draining off the land and all the groundwater moving underneath the land drain into common waterways within the boundaries of the watershed (lakes, rivers, wetlands, groundwater).
All lands and waterways are within a watershed. Watersheds (and the waters that flow through them) are also connected to each other; smaller watersheds drain into larger watersheds. The map to the right shows where all of Wisconsin's water (small watersheds draining into larger ones) eventually flows.
Starting as rain falling on the ground or melting snow, all water in your watershed works its way "downhill" and in Wisconsin ultimately enters the Great Lakes or the Mississippi River. The map (right) shows the three major drainage patterns in Wisconsin. Areas shaded brown drain to Lake Superior, areas shaded purple drain to Lake Michigan, and areas shaded yellow drain to the Mississippi River.
Much of the precipitation that falls on the land is taken up and used by plants. Excess water that is not absorbed into the soil may run off the land quickly into lakes and streams. Precipitation that soaks into the ground can work its way through the soil where, as it continues to move downward, it will ultimately enter groundwater. Depending on the path, the trip water takes from the watershed into the lake can take a few days or many, many years. 