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Eurasian Watermilfoil

(Myriophyllum spicatum) 

A genuine threat to our lakes

This aquatic plant is a genuine threat to our lakes.  Originating from Eurasia, it is present in more than a hundred lakes in the province of Quebec.

Both an emergent and submergent plant, it is rooted to the substrate, can grow to depths of up to 10 meters and form dense grass beds.  There are six species of native watermilfoil.  A good way to differentiate them from the alien species is by observing their leaflets.  If there are more than 15 pairs per leaf, it is most likely the Eurasian Watermilfoil variety.  In addition, the stems are abundantly branched and close to the water’s surface.

In order to tell it apart from other indigenous species, please consult the Eurasian Watermilfoil fact sheet prepared by the  MELCC.











Image source: MELCC


Many have described the Eurasian Watermilfoil as a « zombie plant » because of its extremely invasive method of propagating.  This macrophyte reproduces through fragmentation, that is to say that it only takes one small piece of plant to generate a whole new specimen.

In this way, in just a few years, this plant can form huge, very dense grass beds, compromising the biodiversity of the lake, in terms of flora and fauna.  It smothers the other species of aquatic plants and invades the habitats of fish and some invertebrates.

These large grass beds can also harm bodies of water aesthetically (bad odors due to decomposing plants, dense meadows of brown plants, etc.) as well as hindering aquatic tourist activities (swimming and boating).


At present, the Eurasian Watermilfoil has not been seen in the lakes of the Municipality of Rawdon.  However, do not let your guard down because some of our lakes are shallow and their watersheds relatively inhabited, making them more susceptible to invasion.

Prevention is essential in thwarting the spread of this plant in our municipal waterways. Its carriers can include boaters and their crafts (motorboat, personal watercraft, sailboat, kayak, pedal boat, trailer, etc.), seaplanes, aquarium keeping (water gardens) and aquatic birds (duck).

To prevent the invasion by an aquatic alien species, please follow the 5 steps listed below every time you enter and exit a body of water:











  1. INSPECT: Before and after taking your boat out of the water, inspect all around your nautical equipment and look for any live plants or organisms that may be attached to it.  Pay special attention to the propellers and the hull of your boat.
  2. REMOVE: Remove any fragments of living plants or organisms (mussels, fish eggs or invertebrates, etc.).
  3. EMPTY: Empty your ballast water or your hold as soon as it comes out of the water.  Drain your holding tanks as well.
  4. WASH: Wash your boat (including your holding tanks) and your trailer with a pressure washer or soapy water.  Use a phosphate-free biodegradable detergent and perform this task at least 30 meters away from any body of water, ditch or sewer manhole.
  5. DRY: If you can, let your boat and equipment dry for at least five days before heading out on another body of water.  This step can replace the washing of your boat if the ambient humidity is less than 65% over the 5 days.


Control method
Pulling and uprooting must be strictly carried out by professional divers.  In fact, fragmentation of the plant can help extend its hold on a lake, rather than eradicate it.  This method can be effective in small areas and should be repeated over several years.  The costs for this method can be relatively high.

When confronted with large colonies, some lake associations resort to the installation of a burlap cloth in the lake bottom to smother this plant.  This method is very costly and its effectiveness has yet to be proven.


For more information, please check out the following links:

  1. CRE Laurentides, Les plantes exotiques envahissantes, le Myriophylle en épis, petit guide pour ne pas être envahi
  2. Espèces exotiques envahissantes – Myriophylle à épis