Eurasian Watermilfoil in McGregor Lake

The Eurasion Watermilfoil is an invasive plant species that has become the number one burden of lakes across Québec and Canada. Nearly uncontrollable, it can attack virtually any lake. This weed infestation lowers property values and undermines enjoyment of the lake. Once introduced in a lake, this plant has the capacity to spread to virtually all areas with depths less than 20 feet. Its mode of propagation is such that the plant spreads at incredible speeds. It has been nicknamed the “zombie plant” due to its ability to multiply even faster once it is cut into pieces. Since the plant can easily reach 3 to 4 meters in length, it can rapidly displace other submerged native aquatic plant species.

The Fédération des lacs de Val-des-Monts produced a report identifying where the weed has been detected in McGregor Lake (2012) and Mud Bay (2015) . See areas in green on the maps.

In 2019, the MLA announced a number of activities to alert residents to the severe impacts of the Eurasian Watermilfoil invasive species in an effort to curtail its spread in McGregor Lake.

  1. Awareness raising was our first priority and efforts included distribution of an info graphic to all members; an information display at the Annual Regatta-BBQ; as well as using the MLA website and Facebook page to provide additional information on this invasive species to MLA members.
  2. The second priority was to undertake a study and update the 2012 mapping of McGregor Lake (adding the part of Courville Bay east of Nadon bridge) and the 2015 mapping of Mud Bay. The non-profit research group Agence de Bassin Versant des 7 (ABV des 7) was contracted to conduct the study and completed the field research by mid-August. It is now preparing the map and compiling the formal report for the MLA.
  3. The third activity we announced was the placement of marker buoys to indicate areas of infestation, however, we noted significant changes in some areas identified in the 2012 McGregor map, and decided to prioritize the 2019 research study and await the results before proceeding with installation of the buoys. We’ll update this site when we have the final results of the 2019 research study, and include the proposed plans for the installation of the marker buoys.

The MLA is working closely with the Fédération des lac de Val-des-Monts (FDLVDM) and five other area lakes (Bernard, Dame, Grand, McArthur, and St-Pierre) to take a watershed-wide approach to curb its spread, and safely remove it from our lakes.

What to look for to confirm it is Eurasian Watermilfoil


This plant has a well-developed leaf system around the stem and can become extremely dense. Its feather-like green leaves are arranged in whorls around the stem in groups of four or five. The leaves have 12 or more thread-like segments (the native northern milfoil has fewer than 12 threads), and tiny pinkish flowers occur on reddish spikes that stand several inches above the water. The leaves have a blunt tip end (the native northern milfoil has a pointed christmas tree shape).  The plant blooms in late July and early August.

This link provides a good description of how to recognize Eurasian Watermilfoil versus other types of weeds.



What are its environmental impacts?

The impacts from Eurasian watermilfoil infestation are numerous and can result in a loss of  biodiversity. Eurasion watermilfoil can cause major physical-chemical changes.  By growing in densely packed colonies, Eurasian watermilfoil creates a zone of stagnation to such an extent that it stops the natural turbulence of the water. As such, suspended particles present in the lake water get trapped within the milfoil clusters and in turn create new sediments rich in nutrition.

During winter, decomposing plants cause a partial de-oxygenation of the surrounding water which can cause the disappearance of numerous species of fish.

During summer, plants reach again for the surface thereby physically blocking the natural water circulation. As a result, water becomes stagnant leading to high levels of coliforms and other bacteria. During photosynthesis of a large number of aquatic plants, the ph level has a tendency to increase. Lakes can therefore attain ph levels of 10 to 15 during the summer which can in turn negatively affect the entire aquatic ecosystem.

Is there a risk to people?

Eurasian watermilfoil plants can form thick mats that make recreational activities such as swimming, water skiing, boating and fishing difficult or impossible, while providing the perfect habitat for mosquitoes.

Water skiing and swimming need to be avoided in the affected areas to avoid spreading it, as well as due to an increased risk of drowning. Boating is also more difficult in such areas, whether by motorized boats or non-motorized, such as sailboats. Getting watermilfoil entangled in boat propellers can cause damage to your boat and increase boat maintenance and repair costs, as well as result in spreading the weed to other areas of the lake.

What you can do to stop the spread

Eurasian watermilfoil plants can continue to live several  days out of the water! Therefore, it is important that once it is safely removed from the lake, it is disposed of in garbage bags.

1. Clean your boat! Since watermilfoil can become entangled in boat propellers, and may wrap around other external parts of your watercraft, you can prevent the spread of it by cleaning your boat before you enter and after you leave any lake or river. If you visit other lakes or rivers, please clean your boat and motor, and empty the water from your hold and livewell before launching it in our lake.

2. Respect the buoys!  Green buoys will be placed to mark the heavily invested parts of our lake. Please avoid these areas. That means no swimming or boating in the area as your propeller and paddles can cut the weed and then spread it to other areas of the lake.

3. Pick up the pieces! Even a small piece of milfoil can take root. Don’t leave uprooted milfoil on your dock. If you see fragments floating by, pick them up and put them in the garbage.

4. Root out the problem! As some milfoil management methods can do more harm than good, please contact before attempting to remove the weed yourself. Please avoid raking & cutting the weed as it causes fragmentation which is difficult to pick up and is the leading method by which the Eurasian watermilfoil proliferates. This method is also not permitted by Québec’s Ministère de l’Environnement et de la Lutte contre les changements climatiques (MELCC). While several techniques and products have been tried to control watermilfoil, the only two methods currently supported by the MELCC (both still require special permits) are:

  • the placement of burlap over the weed, that is weighted with heavy objects (not sand)
  • Diver Assisted Suction Harvesting (DASH) method. The Federation of Lakes of Val-des-Monts is exploring the feasibility of using the DASH method. While more expensive, it is the only approved removal method and has had some success in some northern US states like Vermont, and the Province of British Columbia.

Help us curb the spread of this zombie plant.  Contact if you spot it!