Weed photo taken off a pier on Pewaukee Lake Summer 2009.

What is it?: Eurasian watermilfoil (Myriophyllum spicatum) is an exotic submergent aquatic plant originally from Europe and Asia.  It is an aggressive, rapidly growing plant that displaces native plants and clogs waterways.  Eurasian watermilfoil poses serious threats to the ecological health and recreational value of lakes.  Found in scattered areas throughout the U.S., the plant has recently invaded lakes in central Wisconsin.

Threats to recreation: Eurasian watermilfoil can grow to the surface in waters as deep as 20 feet.  When mature, the plant forms a dense surface map or canopy that may be thick enough for birds to walk on.  Boating, swimming and fishing activities are often inhibited by this mass of vegetation.

Threats to lake ecology: Due to its aggressive early season growth, Eurasian watermilfoil displaces nearly all native aquatic plant species.  Studies have shown that this reduced plant diversity results in a reduced diversity of invertebrates and other organisms that fish feed upon.

Threats to fisheries: The extremely dense plant beds formed by Eurasian watermilfoil provide excellent cover for juvenile panfish – to the point where they are virtually inaccessible to predator fish.  This typically results in overabundant, stunted populations of panfish.  Correspondingly, growth rates of predator fish such as largemouth bass and northern pike are reduced.

Water quality impacts: Stagnant waters low in oxygen are often found in association with dense beds of Eurasian watermilfoil.  The sudden nutrient release caused by the late-season die back of massive plant beds may also cause nuisance algae blooms.

Economic impacts: Millions of dollars are spent annually to control Eurasian watermilfoil.  Left unchecked however, the loss of real estate values and the losses to tourism and recreation-based industries would be far greater.