Milfoil Morning

What has 12 to 21 pairs of leaflets, tangles itself on boat propellers, and doesn’t belong in Minnesota lakes?

Invasive Eurasian watermilfoil (left) has 12 to 21 pairs of leaflets and grows into dense thickets in shallow water.
Native northern watermilfoil (right) has only 5 to 10 pairs of leaflets and grows in sparse patches.

Eurasian watermilfoil is one of the most common aquatic invasive species (AIS) in Minnesota. Originating in Europe, this aquatic plant was accidentally introduced to the United States about 50 years ago and has been spreading ever since. As of January 2018, Eurasian watermilfoil has been found in 22 lakes in Washington County and 12 lakes in Chisago County.

Byron Karns, a ranger with the National Park Service, refers to invasive species as “biological pollutants,” saying “they pollute our local lakes and rivers, but, instead of breaking down over time like other pollutants, they reproduce and spread to new lakes as well.” Each invasive species carries with it a unique set of problems.

Eurasian watermilfoil’s tangled stems grow into thick mats of vegetation that make boating and swimming a pain.  These milfoil mats can also crowd out native plant species that support fish and other wildlife. Once Eurasian watermilfoil takes hold in a lake, it is almost impossible to remove. Furthermore, the plant can take root and establish a new colony from a single segment of stem and leaves. To prevent the spread of Eurasian watermilfoil and other AIS, Minnesota law requires all boaters to clean and drain boats, trailers and other equipment after coming out of the water and to dispose of unwanted bait, including minnows, in the trash.

Since 2015, the Minnesota Legislature has distributed annual funding to counties to help prevent the spread of AIS. This funding supports watercraft inspections, public education, and management activities in infested lakes. This year, Washington County will spend approximately $136,000 in state funding on AIS prevention efforts, including providing several grants to area lake associations to treat infestations of Eurasian watermilfoil.

On Wednesday, April 11, 8:30am-noon, St. Croix River Association will host “Milfoil Morning,” a workshop all about Eurasian watermilfoil. The event will include presentations by Mike Verhoeven of the Minnesota Aquatic Invasive Species Research Center (MAISRC) and Chris Jurek from the Minnesota DNR.  There will also be a panel discussion, featuring local experts and lakeshore residents in Chisago and Washington Counties who have experience battling milfoil in their lakes. “Milfoil Morning” will be held at St. Bridget’s of Sweden Church in Lindstrom.

For more information about Eurasian watermilfoil and other invasive aquatic plants, visit:

To register online for Milfoil Morning, go to: