Protecting the quality of the lake water

Since its beginning, the Association du Lac Mercier has always been focused on the protection of the environment, and numerous initiatives were undertaken to protect the quality and the health of the lake:


  • Cooperation with organizations devoted to the protection of the environment, especially that of lakes, of which:

-Programme des Lacs (1989-1992) sponsored by the Ministry of the Environment of Quebec (ceased activities in 1992)

-Member of the FAPEL (1989-2002) (the organization has ceased activities recently)

-Conseil Régional en Environnent des Laurentides (CRELA) since 1995

  • Request to the municipality for a limnology study (2000)
  • Surveillance of “milfoil” growth (since 2003)
  • Request for city interventions to limit the spread of milfoil (washing of boats, identification of growth clusters, etc) since 2003
  • Commissioning of three studies of the littoral zone, measuring the quality of the lake water, by Louise St-Cyr, biologist (2003, 2007 and 2008)
  • Identification of measures to contain and limit the deposition of phosphorus in the lake, following the appearance of blue algae growth  (cyanobacteria) in 2007

  • Collaboration with the Department of the Environment of the city, in their program of evaluating the quality of Lac Mercier (2004)
  • Participation in the Volunteer Lake-Monitoring Program  (VLMP)

What is Voluntary Monitoring of Lakes Program (VLMP)?

  • An environmental analysis of the tributary streams flowing into lac Mercier, scheduled for 2011, has been postponed.
  • In August 2008, the association sponsored an “Evaluation of the littoral zone of lac Mercier”. The study biologist, Louise St-Cyr, identified several dense mats of invasive plants (Eurasian water milfoil, Broad-leaved Pondweed, Elodea). Two large dense mats, composed mostly of Eurasian water milfoil, were identified:

– One dense cluster located near the rock island in front of the public beach

– One dense cluster in the north-west portion of the lake

– Several smaller growths were also found mostly in the southern part of the lake

The study concluded that there were invasive plants in 6 of the 9 sectors that were sampled.

Several measures have been taken by the Association du lac Mercier since its’ beginning, in order to protect the quality and the health of the lake, but constant involvement is required. The Association is very active in the following projects:

  •  Participation in the Volunteer Lake-Monitoring Program   (VLMP)

Program in cooperation with the Ministry of Long-term Development, Environment and Parks, and with financial support from the City of Mont-Tremblant.

  •   City of Mont-Tremblant’ s five-year follow-up program on the health of the lake.  

A summary of the 2012 experts’ report confirms that the quality of the water in lac Mercier has improved since that last study done 5 years ago.

Compared to other lakes in the municipality, our results place us among those in the best health. These results were achieved by the efforts of all the residents, as well as by measures instituted by the city. This should be a proper motivation to keep up all of the residents’ good efforts !

The complete report is available on the web-site of the City of Mont Tremblant.

Programme d’évaluation et de surveillance des lacs -City of Mont-Tremblant


  • Identification of the main species of invasive plants present in the lake:


Invasive Plants Description:

Eurasian water milfoil:

Because of it’s rapid growth, from the first days of Spring, Eurasian water milfoil create dense mats producing shade that inhibits the growth of other submerged plants.

Eurasian milfoil’s mats are known to become so dense as to displace all other plant species. (Environnement Canada, 2003).

  Since Summer 2010, we have observed that the Eurasian water milfoil cluster near the rock island has spread widely towards the south, creating a major cluster of Eurasian water milfoil in lac Mercier.

  • Localization of the most important clusters, by the installation of buoys:

Eurasian water milfoil spreads naturally when cuttings are spread by wind and waves, a process greatly worsened by the passage of watercraft.

The propellers of motorboats, pedal boats and even rowboats, slicing through dense eurasian milfoil mats, significantly accelerates the spread of this plant.

It is therefore very important to identify the sites of these growths, so as to avoid navigating through, or even swimming in them.


The milfoil cluster near the island in front of the beach was marked by the Association du lac Mercier in July 2013 with two buoys. Another cluster was found in August 2013, and third buoy was placed.

During Summer 2016, the situation has worsened because the milfoil clusters have spread and densified in the area adjacent to the municipal beach, as you can appreciate from these photos taken on September 5, 2016.


Summer 2017: milfoil cluster near the municipal beach The milfoil cluster near the municipal beach has enlarged, and the one near the rock island has densified.


Photos taken September 11, 2017 by Lucie Hétu.


  • Filtration marsh

During Summer 2012, the municipality has completed repair work on the storm sewers of the village streets, and the lac Moore stream, both of which now flow into a drainage filtration pond near rue Plouffe. Evaluations of efficacy will be done on a regular basis.


During Summer 2017, we observed that the filtration marsh on chemin Plouffe was filled with sediments from water drainage, occurring over several years.

The marsh filled with sediments no longer fulfills its filtration function. Water originating in lac Moore and the storm sewers now flows directly into lac Mercier. The marsh has been abandoned, and no funds for maintenance have been budgeted in 2017 by the city of Mont-Tremblant.

The city has confirmed that the filtration marsh will be emptied of sediments, and the plants replaced at the beginning of July 2018.


Back to   Residents get involved in an Association