PAST, PRESENT, AND FUTURE OF EURASIAN WATERMILFOIL IN THE MANITOWISH CHAIN OF LAKES

Jamie VandenLangenberg, Water Program Director, NLDC

Eurasian watermilfoil was first detected in the summer of 2023, rooted in the Lower Trout River channel between Alder and Manitowish Lakes. Since then, it has spread rapidly. By the end of 2024, rooted plants were confirmed in Manitowish, Little Star, Alder, Spider, Stone, and Fawn Lakes. Findings from late-season 2023 and early-season 2024 mapping were used to guide targeted removal efforts in July 2024, focusing on the densest colonies in the Lower Trout River. These efforts involved mechanical Diver-Assisted Suction Harvesting (DASH), carried out by Aquatic Plant Management, a private contractor. Meanwhile, the North Lakeland Discovery Center’s Woods and Water team manually pulled smaller infestations.

The extent of plant growth and the rapid expansion of the Eurasian watermilfoil population exceeded expectations. This may be due to the mild winter, low snowfall, and early ice-off conditions from the previous year. As a result, the decision was made to survey all lakes in the chain and manually remove any Eurasian watermilfoil found, unless it appeared in substantial, colony-sized patches

Late-season surveys conducted by the Woods and Water team in Rest, Island, Wild Rice, Clear, Vance, Benson, and Sturgeon Lakes found no presence of Eurasian watermilfoil. However, Stone, Fawn, Alder, Little Star, and Spider Lakes all showed varying degrees of infestation. While smaller in scale compared to the Lower Trout River and Manitowish Lake populations, Spider Lake showed the most growth after these two bodies of water. All rooted plants found in Little Star, Upper Trout River, Alder, Fawn, and Stone Lakes were manually removed, with nearly all plants in Spider Lake also being hand-pulled, except for some near the channel to Manitowish Lake.

Looking ahead, the goal is to develop a comprehensive Eurasian watermilfoil management plan for the entire chain of lakes. Onterra, LLC, a professional lake consulting firm, will be guiding the Manitowish Waters Lakes Association through this process, aiming for plan completion by late summer 2025. In the meantime, efforts will continue, with hand-pulling targeting smaller infestations and DASH techniques focused on dense colonies.