We focus on water quality and watersheds to manage lakes. This includes: applying alum, harvesting plants, installing rain gardens, monitoring, sweeping streets, and treating stormwater. For questions or more information, email This email address is being protected from spambots. You need JavaScript enabled to view it. or call (651) 675-5300.

Applying Alum

Dense algae and aquatic plants decrease lake recreation and aesthetics. These conditions can result from high phosphorus levels in the water and sediment. We apply alum (aluminum sulfate) to put lakes on "diets" by reducing phosphorus. Alum settles through the water and into the sediment, where it binds with phosphorus. For a limited time, lakes turn milky-blue and very clear. The water is safe during applications.

Alum is not an herbicide. It reduces the potential of dense algae and plant growth. Lakes may have less algae after alum applications. But with clearer water, they may have more plants. Aquatic plants help stabilize and protect lake bottoms and maintain water clarity. We use alum to improve water quality and to protect lakes in the long term. Alum benefits should last 5 to 10 or more years. We track alum-treated lakes to check longevity and potential future applications.

Harvesting Plants

The State of Minnesota regulates removal of aquatic plants from lakes. Our permits allow harvesting up to 50 percent of a lake's surface area. We operate large machinery to benefit recreational access. We can launch only on Blackhawk, Fish, Holz, Schwanz, and Thomas lakes.

Plant Harvesting in Eagan Lakes (3 m. 38 s. video)

Installing Rain Gardens

We built 25 rain gardens to filter and absorb stormwater runoff to benefit Schwanz Lake. The rain gardens reduce runoff from the neighborhood by about 60 percent. Stormwater utility fees, Dakota County, and a Minnesota Clean Water Fund grant funded the project. Here's more information about rain gardens.


Excessive phosphorus affects the water quality of lakes and wetlands. Algae and aquatic plants thrive on phosphorus. As these plants decay, oxygen in the water can drop to levels stressful to sensitive fish. Impaired water quality decreases lake recreation and aesthetics and property values.

We collect data and samples of lake water from May through September. We analyze samples for phosphorus and algae levels. Instruments measure pH, dissolved oxygen, conductivity, temperature, and transparency. We assess long-term trends.

Sweeping Streets

Street Sweeping

Treating Stormwater

We reduce phosphorus before stormwater enters lakes in some cases. A special facility uses alum to reduce stormwater phosphorus to benefit Fish Lake. We operate this facility through a Minnesota Pollution Control Agency permit. Other special sand filters improve the abilities of ponds to clean stormwater. Enhanced with iron, the filters reduce phosphorus.