Eurasian watermilfoil

Eurasian watermilfoil

Image Credit: Allison Fox, University of Florida

Eurasian Watermilfoil

Myriophyllum spicatum


Eurasian watermilfoil, a submerged aquatic in the Haloragaceae family, is an invasive that prefers stagnant to slow-moving water. It can be easy to misidentify native milfoil species as invasive due to their close resemblance to their Eurasian counterparts. So, some of the key characteristics you should look for when suspecting Eurasian watermilfoil (EWM) lie within the plant's leaves:

  • whorls (circles) of four delicate feather-like leaves around its stem, and usually 12-21 leaflet pairs per leaf as opposed to native northern watermilfoil which has more rigid leaves with only 5-10 leaflet pairs per leaf. 
  • notice the often bright green color distinct to the EWM  
  • rooted in lake or river bottoms, their stems will grow toward the water surface, usually reaching lengths of 3-10 feet
  • EWM collapses when pulled from water, while native milfoil maintains structural integrity out of water
  • forms dense mats which restrict light availability for native species

Note: As mentioned, EWM prefers stagnant to slow moving water, thus you’ll often find it invading ponds, lakes, and/or slow moving streams. 

For more information visit Midwest Invasive Species Information Network (MISIN)

Eurasian watermilfoil leaves

Feather-like leaves of Eurasian watermilfoil

Image credit: Graves Lovell, Alabama Department of Conservation and Natural Resources

Eurasian watermilfoil underwater

A view of EWM underwater

Image credit: Robert Johnson, Cornell University

mat of Eurasian watermilfoil

A dense mat of EWM

Image credit: Leslie J. Mehrhoff

Eurasian watermilfoil on a boat

EWM can easily hitch-hike on watercraft

Image credit: Tip of the Mitt Watershed Council

KISMA Management Practices

Unfortunately, Eurasian watermilfoil is already established within the Keweenaw and the majority of the continental United States. It has been detected within the Keweenaw waterway, and cases have even been reported on Isle Royale. Management of EWM is heavily dependent on early detection and prevention because once it takes hold of a site, it can be incredibly difficult to eradicate. New colonies often appear near boat landings or other disturbed sites, and hand pulling or raking is an effective way to remove these smaller patches. However, once a body of water is taken over by EWM, not much can be done outside of widespread chemical treatment or bottom screening, both of which require permits and can damage native species. In order to prevent these infestations, make sure to follow these state mandated steps when traveling between waterways in the Keweenaw:

  1. clean boats, trailers, and equipment of any visible plant fragments
  2. drain ballasts or any other water from boats, trailers, and equipment
  3. dry boats, trailers, and equipment 
  4. learn how to identify EWM, and monitor access sites, marinas, or inlets for the first sign of invasion

Note: Eurasian watermilfoil can spread via fragments, so even one small stem fragment can take root and form a whole new colony. It is crucial that all plant matter is removed before you travel from waterway to waterway.