Quality of the lake water

Several measures have been taken since the beginning, in order to protect the quality and the health of the lake, but constant involvement is required.

List of initiatives related to the health status of the lake

This page is available on the website petitehistoiredulacmercier.ca

eau1Quality of lake water and protection of the lakebed

The association du lac Mercier 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.

What is Voluntary Monitoring of Lakes Program (VLMP)?

Slide9  Water Transparency results 2018:

Comparative results since 2009:

An aquatic environment weak in nutritive elements is said to be “oligotrophic “. The elements measured during Summer 2017 determined the trophic level of lac Mercier:

Conclusion of the VLMP en 2017 :

-“The lake is classified as “oligotrophic” i.e. poor in nutritive substances,

 -Lac Mercier shows few signs of eutrophication”.  (therefore, no deterioration).


-Lake to be protected

-Limit the leaching of nutritive substances from human activities.

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

 Brief summary of the 2012 experts’ report:

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.

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

This should be a proper motivation to keep up all of our good efforts !


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



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

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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.

A map identifying the Eurasian water milfoil growths is up-to-date, and available.

Map of lac Mercier showing dense milfoil clusters:

Identification 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 Eurasian water milfoil dense 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 in July 2013 by two buoys. Another cluster was found in August 2013, and third buoy was placed.

Facing expansion of the milfoil clusters, the Association decided to buy 3 more buoys in order to mark the enlargment of the milfoil clusters.

The Association is working closely with Ville de Mont-Tremblant and the local businessmen who rent kayaks and stand-up paddle crafts, as well as the swimmers and others who frequent the municipal beach, so that they avoid the milfoil zones marked by buoys.



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 island has densified.:

Photos taken September 11, 2017 by Lucie Hétu.

New guide available:
Filtration marsh
  • Storm sewer

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.

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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 since 2017 by the city of Mont-Tremblant.

Consequently, the filtration marsh will not be emptied of sediments, and the plants will not be replaced.

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