Aquatic plants

The Eurasian watermilfoil

What is milfoil?

Eurasian watermilfoil(Myriophyllumspicatum) is an invasive exotic aquatic species from Europe and Asia. It was introduced and distributed in Quebec most likely as an ornamental plant for artificial ponds.

It has been present in Lake Massawippi since the early 1960s. It is spreading exponentially for 3 reasons (Lavoie 2019):

  1. Lack of natural predators;
  2. Early growth in spring;
  3. It reproduces mainly by fragmentation. In the natural environment, towards the end of the summer, adventitious roots grow along the stem. Then, helped by the waves, the plant sections off segments which drift away and settle elsewhere to form a new plant. This method of reproduction is greatly accelerated by boat traffic.

In Lake Massawippi

Although Eurasian watermilfoil has been present throughout Lake Massawippi for over 50 years, two aquatic plant assessments conducted in 2005 and 2015 lead us to the conclusion that its presence continues to increase year after year.

Annual monitoring since 2015 indicated a strong increase in 2018 and 2019 in certain areas. In general, Eurasian watermilfoil is found along most of the eastern shoreline. In other areas, it is found on shoals and at the mouths of streams.


The impacts are numerous. Depending on its density, milfoil impedes swimming, boating, fishing and water circulation. It also suffocates native species and alters the entire ecosystem. Another non-negligible fact: milfoil decreases the interest in shoreline property and has a significant effect on property values.


All experts agree that it is unrealistic to eradicate milfoil from Lake Massawippi. Control methods are relatively effective on very small lakes, but never 100% effective.

Control methods for Lake Massawippi will therefore aim to slow its propagation and improve the condition of certain sectors.


Not everything is milfoil. Many native plants must be preserved. Milfoil control cannot be carried out at the expense of the natural ecosystem of Lake Massawippi.

Actions and methods

The first action to consider is, undoubtedly, to limit its exponential growth by by restricting traffic in the affected areas.Traffic (even at low levels) is at the root of fragmentation. Boating in the milfoil beds is definitely the best way to lose the battle. This simple and not overly restrictive action attacks the problem at the source. It will not eradicate established milfoil, but it will reduce its growth and reproduction in other areas.

Any direct intervention in aquatic plant beds requires a permit (you can find the Permit Application Form here) from the Ministère de la Forêt, Faune et Parcs (source MFFP, June 26, 2020).

In order to obtain this permit, an assessment of the proposed area must demonstrate that Eurasian watermilfoil constitutes more than 70% of the plants in the area. Blue Massawippi can update this inventory for you,contact us..

This permit is expensive. The solution is to join together with other residents interested in the same request, with the possible participation of the municipality. This is Blue Massawippi’s approach for the current Bacon’s Bay project.

Manual removal

This method is feasible on small areas. However, it requires the complete removal of the roots and the removal of the milfoil from the water body. Manual removal can be very effective and affordable when combined with another control strategy, such as targeting patchy, low-density beds. Large-scale projects requiring divers and a plant vacuuming system are very costly and involve delicate work.

Installing tarps made of burlap or Aquascreen©

These tarps suffocate all the plants underneath, allowing the space to be recolonized by native plants. Regular maintenance (ex: manual removal of plants from the tarps) is also necessary to avoid the re-establishment of milfoil. The effectiveness of the tarps decreases when they are installed in areas of high milfoil density, but this method still provides the most sustainable results for a given price.


An aquatic plant mower cuts plants at a specific height (ex: 2 feet below the surface). This method, while providing rapid results, is rarely viable in the long term (Lavoie, 2019). It will not eliminate the milfoil; it will simply grow back like a lawn. Thus, mowing it several times annually is required to keep the plant in check. The fragments that inevitably escape collection will have a devastating contaminating effect This very expensive method is ecologically unsustainable for Blue Massawippi..

Lowering the lake level in winter

Although this method is considered effective (Lavoie, 2019), it would be impossible to implement in Lake Massawippi. The water level of the lake is regulated and it would take an exhaustive legislative effort, in addition to the support of all 5 municipalities, to even hope to make any changes to the established seasonal targets. In addition, due to the clarity of the lake water, Eurasian water milfoil is present at depths greater than 10 m. Therefore, it would be logistically impossible to lower the lake to a level that would allow eradication. Even if the lake was lowered a few meters, the milfoil would easily be able to recolonize the cleared areas.

Water aeration

This new technique is based on the joint effect of water aeration by microbubbles and the introduction of bacteria that require high levels of oxygen to proliferate. In theory, the bacterial population will reach extremely high densities in the presence of oxygenated water and will thus sequester all the nutrients necessary for the growth of milfoil. This technique is expensive and there is no evidence that it is effective in controlling Eurasian watermilfoil in a systematic manner (Lavoie, 2019). Certain projects report decent efficacy while others did not observe any difference.



Scientific reference: Lavoie, C., 2019.50 Plantes envahissantes : protéger la nature et l’agriculture. Les publications du Québec. Québec. p. 250-257., RAPPEL, Ministère des Forêts, Faunes et Parcs.

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