Ecology

Eurasian Watermilfoil

An aggressive invasive aquatic plant that forms dense surface mats, displaces native vegetation, and impairs swimming, boating, and fishing.

What It Means for Your Lake

Eurasian watermilfoil (Myriophyllum spicatum) is a submersed aquatic plant native to Europe, Asia, and northern Africa that has become one of the most widespread and problematic aquatic invasive species in Minnesota and Wisconsin lakes. The plant has finely divided, feather-like leaves arranged in whorls of four around the stem, and it grows rapidly from lake-bottom sediments to the surface, where it forms dense canopy mats that can cover acres of lake surface. Eurasian milfoil spreads primarily through fragmentation, small stem pieces break off, drift to new locations, and root to form new colonies. A single fragment as small as a few inches can establish a new population. Boats, trailers, and fishing equipment are the primary vectors for transporting fragments between lakes. In Minnesota and Wisconsin, Eurasian milfoil has been documented in hundreds of lakes, with new infestations confirmed each year despite aggressive prevention efforts. The ecological impacts are significant: dense milfoil stands shade out native aquatic plants, reduce dissolved oxygen in the water column at night, create stagnant conditions favorable to mosquito breeding, and alter fish habitat by replacing diverse native plant beds with monoculture stands. Recreational impacts include tangled boat propellers, impeded swimming, snagged fishing lines, and degraded aesthetic quality that can reduce waterfront property values. Management options include mechanical harvesting (cutting and removing plants), herbicide treatment (typically using 2,4-D or triclopyr), biological control using the milfoil weevil (Euhrychiopsis lecontei), and hand-pulling in small infestations. No single method provides complete control, and most lake associations use integrated approaches combining multiple techniques.

Frequently Asked Questions