Management

Watershed

The entire land area that drains water, sediment, and nutrients into a particular lake, the primary factor determining lake water quality.

What It Means for Your Lake

A watershed (also called a drainage basin or catchment) is the total land area from which precipitation, snowmelt, and groundwater flow into a specific lake. Every lake has a watershed, and the size, land use, soil type, and topography of that watershed are the primary determinants of the lake's water quality. In Minnesota and Wisconsin, lake watersheds range from less than 100 acres for small seepage lakes (which receive most of their water from direct precipitation and groundwater) to hundreds of square miles for large drainage lakes connected to rivers and streams. The watershed-to-lake area ratio is a key predictor of water quality: lakes with large watersheds relative to their surface area receive proportionally more nutrient runoff and are more susceptible to degradation. Agricultural land use is the strongest predictor of poor lake water quality in the Upper Midwest, watersheds with more than 50% cropland typically deliver enough phosphorus to push lakes into eutrophic conditions. Forested and wetland-dominated watersheds generally produce the cleanest lakes. Watershed management is the foundation of lake protection because it addresses the root cause of water quality problems: what happens on the land flows into the lake. Effective watershed management includes maintaining vegetated buffer strips along shorelines and streams, controlling agricultural runoff through conservation practices, managing stormwater from developed areas, and preserving wetlands that act as natural nutrient filters. Minnesota and Wisconsin both have organized watershed districts and lake management districts with taxing authority to fund watershed protection and restoration projects.

Frequently Asked Questions