Aquatic Weed Management

In 2021, the South Washington Watershed District (SWWD) oversaw an aquatic plant survey on Colby and Markgrafs Lakes. The results of the survey showed there are varying levels of the invasive aquatic plant species curly-leaf pondweed and Eurasian water milfoil in the lakes.

Eurasian watermilfoil and curly-leaf pondweed form dense mats at the water’s surface, which inhibit water recreationists and demand additional staff resources to ensure mats do not obstruct lake outlets. They also overtake habitat, outcompete native aquatic plants and provide unsuitable shelter, food and nesting habitat for native animals.

In response to the aquatic plant survey findings, the SWWD and a contractor will apply an herbicide to Colby Lake to treat Eurasian water milfoil and curly-leaf pondweed in October.

The treatment will improve the recreational, natural and aesthetic values of the lake. There will be no restrictions to using the lake and the fishing pier will remain open. Signage will be posted at the time of treatment. Further treatments of the lake may be necessary in the future to keep the invasive species under control.

Questions can be directed John Loomis, water resource manager, at 651-714-3714 or [email protected].

For more specific information on the herbicide treatments in each of the lakes, please the SWWD website.