Eurasian Water Milfoil

Eurasian Watermilfoil (EWM)

Where does EWM grow naturally, and how did it get here?
EWM is native to Europe. It spread to North America primarily by boats, and continues to move from lake to lake in Wisconsin by boats.

How do I identify EWM?
EWM has very tall stems, giving it a rope-like appearance. Its leaves are greyish-green, and has finely divided, feathery leaflets. The leaves are arranged in whorls. There are more than 12 leaflet pairs per leaf. EWM looks very similar to native milfoils. You must count the number of leaflet pairs to distinguish native milfoils from the invasive EWM (see images below).
If you suspect you have found EWM in your lake, please contact our Water Program Coordinator for verification.

To identify EWM, count the number of leaflet. Counting them here, notice EWM has more than 12 pairs.

Do not mistake EWM with its native look-alike, Northern Water Milfoil. Notice the native milfoil has fewer than 12 leaflet pairs.

How does EWM impact a Wisconsin lake?
The effects of EWM vary in each lake. Often times, EWM forms thick underwater mats, and can often result in surface matting. This blocks sunlight from native plants. EWM grows very quickly and can out-compete native plants.
One key factor in EWM’s ability to take over a system is that it reproduces via fragmentation. A single inch-long piece of EWM can float away, and take root to form a new colony in another location. Mechanical clearing of aquatic plants for docks, beaches, and landings, has the potential to create thousands of new stem fragments.

Surface matting of EWM

What can be done once EWM enters a water body?

Treatment of EWM can vary on a lake by lake basis. Because EWM may hybridize with native milfoils, it may respond differently to chemical treatments depending on the system. Some lakes have had success with nonselective chemical treatments. Permits are required for chemical treatment.
Hand pulling smaller populations may also be an effective removal method. Your lake group could hire professional divers, or organize a volunteer group to pull EWM. Extreme care must be taken when hand pulling EWM, as even a small fragment can float away, re-root, and start a new population.