Questions and answers about Eurasian watermilfoil

Here are some common questions about Eurasian watermilfoil, with answers provided by the Minnesota Department of Natural Resources (DNR).

Q. What is Eurasian watermilfoil?

A. It is a non-native, invasive submersed aquatic plant that is native to Europe and Asia. It was discovered in the eastern U.S. sometime before 1950. In Minnesota, it was first recorded in Lake Minnetonka in 1987.

Q. How do you identify it?

A. Eurasian watermilfoil typically has 12 to 21 pairs of leaflets. The native northern watermilfoil, with which it is often confused, usually has five to nine pairs.

Q. Why is it a problem?

A. Milfoil can interfere with recreational and other uses of lakes and rivers by producing dense mats at the water’s surface. These mats are similar to, but can be more extensive than, those produced by native vegetation. Matted milfoil can displace native aquatic plants and alter environmental conditions, which in turn may harm fish and wildlife.

Q. Where is milfoil a problem?

A. In Minnesota, milfoil has caused problems in lakes by producing extensive mats where water depths are less than 15 feet, water clarity is high (mid-summer Secchi disk readings of six feet or more), and the fertility of the bottom ranges from moderate to high.

Milfoil has not caused extensive problems in every body of water where it is established. Milfoil generally does not produce mats at the surface in water more than 15 feet deep. In lakes with low water clarity (mid-summer Secchi disk readings less than six feet), milfoil has not produced mats in water more than six feet deep, if at all. In areas of lakes where the fertility of the bottom is low, for example in sandy areas, the growth of milfoil and aquatic plants in general tends to be low.

Q. When is milfoil a problem?

A. Milfoil may cause problems in a lake one year, but not the next. This appears to be mainly due to the weather, which can cause variations from year to year in environmental conditions in lakes, especially clarity, temperature, and depth of water. These in turn can cause large variations in the abundance of aquatic plants, including milfoil.

Q. What can be done about problems?

A. Problems caused by milfoil can be managed by treatment with herbicides or mechanical removal of plants. On lakes where matted milfoil causes unavoidable problems in public-use areas, the DNR offers limited funding for control by lake associations or local units of government. Funding is available only to organizations on lakes that have public water access.

Q. How does it spread?

A. Milfoil is believed to spread from one body of water to another primarily by the unintentional transfer of plant fragments, primarily on trailered boats.

Q. What can be done to prevent spread?

A. The most important action that you can take to limit the spread of milfoil and other aquatic invasive plants is to remove all vegetation from your watercraft before you move it from one body of water to another.

If you think that you have found a new infestation of Eurasian watermilfoil, contact the DNR. In Douglas County, contact Nathan Olson at (218) 739-7576, extension 259. It is very helpful to send a sample of the suspected milfoil plants to the DNR for identification. Put suspected milfoil in a zip-loc bag and mail it to the regional contact.

Q. Regulatory classification

A. Eurasian watermilfoil and its hybrids are classified as prohibited invasive species in Minnesota. It is illegal to possess, buy, sell, transport, and introduce.

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