Eurasian Water-Milfoil: A Closer Look at an Invasive Plant

When we think of invasive species in the Great Lakes basin, aquatic animals often jump to mind: zebra mussels coating a lake bottom, sea lamprey boring holes in fish, Asian carp leaping out of the water in droves as boats travel through waterways. Invasive plant species, however, can be just as impactful on ecosystems as fish, or other aquatic creatures. In particular, this month’s blog post is all about one of the most widespread invasive plants in North America: Eurasian water-milfoil.

Eurasian water-milfoil is an aquatic plant originally from Europe, Asia, and North Africa. Introduced to North America in the mid-19th century likely via ship ballast water or aquarium waste, it was first found in Lake Erie in 1961. Since then, it has spread to all of the Great Lakes, as well as many lakes in southern and central Ontario. Georgian Bay is no exception, as residents of numerous communities along the Bay have identified Eurasian water-milfoil in their areas.

What is Eurasian water-milfoil?

Eurasian water-milfoil is an aquatic plant characterized by its feathery strands, rapid growth, and ability to root in both shallow (1 to 3 meters) and deeper waters (up to 10 meters). It is a perennial, meaning it will grow back year after year, and forms dense mats of vegetation, like the one shown below.

These rapid-growing mats can choke out native plants, reduce oxygen levels in aquatic environments, and clog waterways impeding boating and other recreational activities. Eurasian water-milfoil can also sprout from severed stems, so when plants are chopped up by motorboat propellers or other means, the pieces can take root elsewhere and spread the plant further.

What can I do about it?

While there are programs being run to target and remove Eurasian water-milfoil, we can do our own individual parts to reduce its spread. The two most effective ways of fighting Eurasian water-milfoil are reporting sightings to the right organizations, and reducing our own likelihood of helping it spread.


If you encounter Eurasian water-milfoil, the Ontario government suggests reporting the sighting either via their invasive species hotline, 1-800-563-7711, or reporting the sighting online at EDDMapS, or the Early Detection and Distribution Mapping System, can be used to report sightings of invasive species, either through a web browser at home, or in the moment via their app.

Help reduce the spread

To help stop the spread of Eurasian water-milfoil, boaters and other watercraft owners should practice the clean, drain, dry procedure. When moving your watercraft from one body of water to another, there’s a chance of accidentally bringing small parts of Eurasian water-milfoil (along with other aquatic plants) along for the ride. To avoid this, make sure that you:

Clean your watercraft, trailer, and gear, to make sure it’s free of any mud, sand, or plant material. Rinse, scrub, or power-wash your watercraft away from storm drains or waterways.

Drain your watercraft of any water it picked up from your trip. This includes (but is not limited to) ballasts, bait buckets, bilges, and internal compartments that could hold onto water.

Dry your watercraft and gear thoroughly before moving onto your next trip.

For more information about the clean, drain, dry procedure and more information on invasive species, visit

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