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)?

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 results of the monitoring during Summer 2024:

 

Physical chemistry

  1. An excellent estimate of the average summer transparency of the water was obtained by 14 measurements of the depth of the Secchi disk. This transparency of 5.8 m characterizes clear water. This result places the trophic state of the lake in the oligo-mesotrophic transition zone.
  2. The average trace total phosphorus concentration measured is 3.2 μg/L, indicating that the water is very poorly enriched with this nutrient. This result places the trophic state of the lake in the ultra-oligotrophic class.
  3. The mean concentration of chlorophyll a is 1.8 μg/L, indicating a medium with low microscopy suspended algal biomass. This result places the trophic state of the lake in the oligotrophic class.
  4. The average dissolved organic carbon concentration is 3.9 mg/l, which indicates that the water is slightly coloured. Colour therefore probably has a small impact on the transparency of the water.

Trophic status and recommendations

  1. All the physicochemical variables measured in one of the deep-water areas of Lake Mercier place its trophic status in the oligotrophic class. The summary of the results of the monitoring years is illustrated in the multi-year fact sheet.
  2. Based on the results obtained, Lake Mercier shows little or no signs of eutrophication. This lake must be protected. In order to preserve its condition and uses, the MELCCFP recommends the adoption of preventive measures to limit the intake of nutrients from human activities.

 


An environmental study of lac Mercier, commissioned by the Board of directors of ALM with the support of Ville de Mont-Tremblant, was carried out in 2021 by OBV-RPNS:

   Executive Summary of the Environmental Study of lac Mercier:

 

Rapport d’étude lac Mercier- Ville de Mont-Tremblant 2018


 

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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The Association du Lac Mercier has been working closely with the city of Mont-Tremblant since 2022 to systematically uproot the watermilfoil stems found in the lake.

Jean-Louis Courteau 2023

Read the Diver report- August 2023:

Jean-Louis Courteau 2023

 

The program launched in 2022 to eradicate the watermilfoil from the lake, continues.

 

Here is a summary of the inventory of Guillaume Gendreau-Lefèvre, biologist of the City of Mont-Tremblant, made in August 2024:

  1. The inventory was carried out on August 1 & 2.
  2. We cruised at low speed around the lake as well as in shallow water (until the bottom was no longer visible) paying particular attention to the places where the milfoil was recorded in the past;
  3. In total, we listed about a hundred stems (a plant could be composed of a single stem as well as 5 stems);
  4. We did not see any large clusters;
  5. Most of the plants were not visible from the surface (we used aquascopes and snorkelers to increase our chances of spotting the MAE).


 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.

Following multiple requests from the lake association, the filter marsh was finally cleaned in the autumn of 2024 and emptied of its sediments and suspended solids. However, plants have not replaced.