Pollutants

Stormwater Runoff

Rainwater and snowmelt that flows across impervious surfaces like roads, driveways, and rooftops, carrying pollutants into lakes and streams.

What It Means for Your Lake

Stormwater runoff is precipitation that does not soak into the ground but instead flows across the land surface, collecting pollutants and transporting them to lakes, streams, and wetlands. In developed areas around Minnesota and Wisconsin lakes, stormwater is a significant source of phosphorus, sediment, road salt, petroleum products, lawn chemicals, and bacteria. Impervious surfaces, roads, driveways, parking lots, rooftops, and compacted lawns, prevent rainfall from infiltrating into the soil, dramatically increasing the volume and velocity of runoff compared to natural conditions. A one-acre parking lot generates 16 times more runoff than a one-acre forest during a one-inch rainstorm. In lakeside communities, stormwater often flows directly into the lake through ditches, storm drains, and shoreline erosion channels. Each rain event delivers a pulse of nutrients and sediment that cumulatively degrades water quality over years and decades. Studies of Twin Cities area lakes have shown that stormwater from developed watersheds delivers 2 to 10 times more phosphorus per acre than runoff from forested or wetland-dominated watersheds. Stormwater management practices designed to reduce lake pollution include rain gardens (shallow depressions planted with native species that capture and infiltrate runoff), permeable pavement (allows water to soak through the surface), vegetated swales (grass-lined channels that slow and filter runoff), and stormwater ponds (detention basins that settle out sediment and allow nutrient uptake). Lakeside property owners can reduce their stormwater impact by minimizing impervious surfaces, directing downspouts to rain gardens rather than the lake, maintaining native shoreline buffers, and eliminating or reducing lawn fertilizer application.

Frequently Asked Questions