Invasive Species

Eurasian Watermilfoil
Myriophyllum spicatum

Eurasian watermilfoil was accidentally introduced to North America from Europe. Eurasian watermilfoil spread westward into inland lakes primarily by boats and also by waterbirds, reaching Midwestern states between the 1950s and 1980s. Unfortunately, Eurasian watermilfoil has invaded many Northern Michigan lakes.

Eurasian watermilfoil is very invasive. In nutrient-rich lakes, Eurasian watermilfoil can form thick underwater sands of tangled stems and vast mats of vegetation at water's surface. These dense weed beds on surface water can impede navigation - and no one likes to swim in areas thick with aquatic plants. Eurasian watermilfoil is bad for the health of our lakes too. The dense beds absorb sunlight causing water temperatures to increase which causes the amount of dissolved oxygen to drop. Smaller fish congregate on the edge of the beds making them more susceptible to predation. Ultimately, as with any aggressive exotic species, native plant and animal diversity declines when Eurasian watermilfoil out competes native aquatic plants. A key factor in the plant's success is its ability to reproduce through stem fragmentation and underground runners. A single segment of stem and leaves can take root and form a new colony. Removing native vegetation creates perfect habitat for invading Eurasian watermilfoil. Eurasian watermilfoil has difficulty becoming established in lakes with well established populations of native plants. In some lakes, the plant appears to coexist with native flora and has little impact on fish and other aquatic animals. Milfoil may become entangled in boat propellers, or may attach to keels and rudders of sailboats. Stems can become lodged among any watercraft apparatus or sports equipment that moves through the water, especially boat trailers.

Plant Identification

Identifying Eurasian watermilfoil can be tricky since it looks similar to native watermilfoils. Eurasian watermilfoil typically has 12 to 21 pairs of leaflets. The native northern watermilfoil usually has 5 to 9 pairs.

Plant Control

There are several techniques that can be used to control Eurasian watermilfoil. Although the native weevil may be one of the safest ways to control Eurasian watermilfoil, it isn't always the least expensive (weevils cost around $1 each). Physical and mechanical methods of control such as harvesting with machines or hand removal or bottom barriers can be effective. The mechanical clearing of weed beds for beaches, docks, and landings creates thousands of new stem fragments. Higgins Lake placed geotextile material over he plant beds this summer with fairly good results. Eurasian watermilfoil spreads by fragmentation of pieces so harvesting must be done very carefully to avoid spreading the plant further.

Ultimately, prevention is the most efficient and least expensive strategy and is appropriate for all lakes where no Eurasian watermilfoil currently exists, as well as where its management is under way. Prevention can entail public education and signage at nearby infested lakes to warn boaters about transport of plant fragments to Eurasian watermilfoil free environments. Please contact the Watershed Council if you would like more information.

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