Aquatic Plants in Blue Sea Lake

- Identification of the ProblemPlanteAqua01
- Methodology
- Nature of the Plant
- How to Fight its Proliferation
- Permits
- Surveillance


Identification of the Problem

Several residents of Blue Sea Lake have expressed concern regarding the presence of increasingly large beds of aquatic plants along the shoreline. This article provides information regarding these plants and how to limit their proliferation.


To answer the questions raised about these aquatic plants, representatives of the Association consulted various authorities within the MRC, the municipalities, ABV des 7 (a regional environmental organization) and the provincial ministry of the environment. These officials provided us with a wide range of information regarding the biological, environmental, and legal aspects of this issue.

masquinongéNature of the Plant

The plant in question is a type of pondweed. Because this is a very large plant family (according to Wikipedia there are approximately 90 varieties of pondweed), we would require very clear, close-up photos of the plant's leaves (which we currently do not have) to identify the specific variety. However, because all members of the pondweed family share several characteristics, we do have a fairly good idea about the nature of the plant.

PlanteAqua03An indigenous plant, the pondweed provides marine fauna with shelter and food. It grows along the shoreline out to a depth of 3 metres. Like the Eurasian milfoil, it can reproduce via various means, which explains why it can spread so easily. These means include:

  • by fragmentation (if it is cut, pieces of it will reroot - like milfoil);
  • by rhizome (a modified stem with nutrient reserves that grows along and below the soil surface, and produces roots and shoots irregularly distributed along its length); and
  • by dispersion of its seeds.

How to Fight its ProliferationFlèche haut bouton

To limit its spread, we must reduce the flow of phosphorus into the lake. This, of course, is easier said than done and remains one of the great challenges of our Association. As a first step, we must identify and eliminate - as best we can - the sources of phosphorus near the shoreline as well as those conditions that facilitate its inflow (eg: fertilizers, compost, septic tanks, runoff, shoreline that has been stripped of its vegetation, etc.). Although reducing the inflow of phosphorus will not provide an immediate solution to the spread of these plants, it is the only way to limit their proliferation in the long run.

In the meantime, we must do all we can to stop the fragmentation of the plant. Accordingly, boaters must avoid weed beds as engine propellers and turbines can easily chop and disperse fragments of these plants. Similarly, bathers, fishers, and other users of the lake must be aware that if they uproot or cut these plants, they will help them spread. If a plant is fragmented by accident, every effort must be made to collect all segments of the plant.


To effect any intervention (no matter how small) in the littoral zone of the lake, you must obtain a permit from the municipality and, in certain cases, from the provincial ministry of the environment (MDDEP). In the latter situation, the request must be submitted by an organization (eg: our Association or municipality) or by a group of individuals who have obtained the consent of the local property owners.

For more information on this subject, please consult the following MDDEP documents (in French):

  • Control of Aquatic Plants and Algae - provides the legislative, regulative, and methodological framework for all interventions dealing with the management or control of aquatic plants and algae.
  • Annex 1 - Aide Memoire on the Control of Aquatic Plants and Algae - provides an idea of what is required when submitting a request to effect an intervention.
  • Annex 2 - Methods of Controlling Aquatic Plants and Algae - offers a summary of currently available methods of controlling aquatic plants and algae. As is indicated in the introduction to this annex, "the Ministry does not advocate the use of the various methods presented". The annex is simply a guide to assist in the analysis of projects submitted to the Ministry.

SurveillanceFlèche haut bouton

There is no simple and effective way to stop the proliferation of pondweeds. That said, some of the authorities we consulted questioned whether the low water levels we experienced in the summer of 2012 may have made the problem appear worse than it is by exposing more of these plants than would usually be seen during a normal summer (ie: the plants have always been there - we just didn't see them).

Whatever the case, it would be very helpful to document the evolution of these plant beds from one year to the next. To this end, RSVL staff members are currently preparing a protocol that will detail how to monitor the growth and spread of aquatic plants. The Association will advise its members as soon as this protocol is made available and will update this article accordingly. In the interim, it would be useful to collect some preliminary data about these beds, specifically: their location (ideally using GPS coordinates or by reference to fixed points such as a cottage, a dock, etc...); the size of their perimeter; their area; their density; and their depth.

PlanteAqua04 en

Photos of the bed would also be most useful. The Association has a camera which can take underwater photos up to a depth of 12 metres; this camera could be made available for this purpose.

The data and photos (if applicable) should be updated at the same time each year (eg: the beginning of August).

A Word of Caution

Be advised that, according to all the experts we consulted, if one were to eliminate the pondweeds (a native species), their place would likely be taken by the Eurasian milfoil - an invasive species that poses a much greater threat to our lake.

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