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September 2023 Blue green algae (cyanobacteria) blooms in Lake Gervais

Dernière mise à jour : 9 oct.

Summary of the situation as of September 26, 2023

  • Blooms of blue-green algae (cyanobacteria) cause nuisance (tastes, odors, skin irritations, etc.) and toxicity, if algal toxins are produced.

  • After the observations of blooms at Lakes Bibitte and Tremblant, preventive advisories were issued by Mont Tremblant and Lac Tremblant Nord.

  • The municipality of LTN initiated activities to confirm the presence of blue-green algae and to verify their toxicity.

  • The presence of a type of cyanobacteria, Gloeotrichia, that forms white flakes in water is confirmed, but no toxicity has been detected by testing at Polytechnique's CREDEAU lab on samples collected Sept 15th and again on Sept 23rd.

  • At Lake Gervais, no significant accumulation has been reported, but scattered white flakes were observed on September 17th. Samples were taken and showed low levels of cyanobacteria sufficient to trigger surveillance for drinking water.

  • Given the absence of toxicity, the risks of consuming drinking water and from contact activities are considered to be very low.

  • Other reports of blue-green algae blooms were made in September in the region. 2023 appears to be a favorable year for the development of blooms.


Recent blue green algae blooms reported in lakes in the Tremblant area in late September 2023

On September 8, 2023, two public press communiqués were issued for Lac Tremblant and Bibitte concerning the 'possible presence of cyanobacteria' or blue-green algae. These observations were reported by local residents and samples sent to the Quebec Ministry of the Environment. A reminder of the precautions for these lakes was made by the municipality of LTN on September 15th.

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While awaiting official results, other samples were taken at Lac Bibitte and Lac Tremblant:

1) as part of the I adopt a lake program at the University of Montreal which measures with great precision a range of cyanobacterial toxins and nutrients (nitrogen and phosphorus). Results will be available in late 2023.

2) by CREDEAU-Polytechnique for the rapid measurement of microcystin by strips and the identification of the cyanobacterial species present by microscopic enumeration. Results will be available the week of September 18th.

Blooms observed at Lac Bibitte and Lac Tremblant involve a cyanobacteria called Gloeotrichia echinulata. These cyanobacteria form colonies, i.e. clusters of several are most probably and cells of a size of 1-3mm which become visible to the naked eye. They can produce toxins, notably Microcystin LR, which need to be confirmed.

Several thousands cells assemble in the form of a ball of filaments as shown in the fluorescence image where each green dot is a cell. They're a bit like miniature lake anenomes!

Gloeotrichia echinulata from Lac Bibitte (Jacinthe Mailly CREDEAU) Sea tube anemove

Microscopic observations at Polytechnique and GRILL show that the blooms are caused by Gloetrichia echinulata in the Tremblant area lakes.

Colones from September 15th and 24th 2023 water sampling (Jacinthe Mailly CREDEAU )

The colonies are visible in the form of small whitish balls (specks) in suspension. These colonies can reach 1-3 mm and are visible in the form of small whitish balls in suspension. Sometimes they are scattered throughout the water column, difficult to distinguish.

photos taken in Tremblant area

Sometimes, they accumulate and form scums near the shore, typically downwind of the dominant winds.

Are such blooms in pristine lakes normal?

Lakes such lakes Tremblant, Bibitte and Gervais are considered pristine and less prone to frequent and intense blooms. However, several recent studies report more frequent blooms of Goeotrichia in northern lakes in Ontario, New Hamspshire, Maine, Poland and Sweden. They occur in lakes with low levels of nutrients such as many of the lakes in the Tremblant region (oligotrophic). Potential causes of blooms include elevated temperatures, changes in nutrients and mixing of lakes.


Information on the presence of blue-green algae (cyanobacteria) at Lake Gervais in 2023

In September, there were no reports of major accumulation of cyanobacteria or blooms at Lake Gervais.

  • On September 9th 2023, there were no reports of accumulation of cyanobacteria or blooms at Lake Gervais. Michiel and I kayaked around the lake on September 9th and did not observe any accumulation of cyanobacteria scum. In addition, we spoke to several local residents on pontoons and a few fishermen. They also did not observe such accumulations.

  • However, white particles were observed in the water on Sept 17th at the end of our dock in the South east area of lake Gervais. Samples were collected and sent for analysis.

  • A composite sample was collected from 4 locations and will be processed. Thanks to our new resident Elaine et her husband for the assistance with their ponton! On September 21st, these white flocs were no longer visible.

  • Scum collected from Lac Bibitte on Sept 15th and 23rd was analyzed for the presence of toxins using quick response strips for the detection for microcystins. Results were below the detection limit of this test (<0,5ug/L microcystins). Additional measurements with a more sensitive methods will be done by the Adopte un lac program of Université de Montreal. As results did not show any detectable toxins even with significant accumulations, the risks of toxicity at Lake Gervais were even lower.

Analysis of toxins at CREDEAU

Lake Gervais Cyanobacteria identification results: Cyanobacteria counts under a microscope are the gold standard method for verifying the number and species of cyanobacteria present. This work was carried out by a GRIL specialist in collaboration with Polytechnique Montréal. The results of Sept 17th samples from Lake Gervais show the presence of 23,857 cells/mL of cyanobacteria (biovolume of 0.14mm3/L). The most abundant species are: Coelosphaerium kuetzingianum, Cyanodictyon imperfectum and Chroococcus prescottii. Only the first species is capable of producing toxins.

These values ​​can be compared to the thresholds used to guide prevention actions. The results can be compared to lake monitoring thresholds for drinking water or swimming. For drinking water, a concentration of 20,000 cells/mL has been proposed as the first level of vigilance with monitoring, while the World Health Organization (2021) recommends a biovolume of 0.3mm3/L. The results from Lake Gervais place us at or below the monitoring limit. For recreation, the thresholds are higher at 4mm3/L. These results indicate that the risk for drinking water and swimming was low at Lake Gervais in September 2023.


Any risks when swimming or drinking the water from Lake Gervais?

Yes, if there is a suspected or confirmed cyanobacteria bloom, it is recommended by the Ministère de l'Environnement du Québec to take these precautions near the bloom:

  • 'avoid swimming, water skiing, windsurfing, diving and kayaking. It is also specified to avoid drinking water, using it for cooking and preparing drinks or ice cubes, using it to brush your teeth, or giving it to your animals.'

In fact, all water sports and drinking water consumption would be affected.


What are cyanobacteria or blue green algae?

Information is available on the website of the Quebec Ministry of the Environment:

'Blue-green algae are microscopic organisms whose scientific name is “cyanobacteria”. They have existed for more than three billion years. The name “blue-green” comes from the dominant blue and green pigments in most species. Some have different colors, like red or brown, but we see them less often.

Blue-green algae are naturally present in Quebec lakes and rivers at low densities. They pose a problem when they multiply too much and form “blooms”. These often resemble a mini-particle soup or broccoli soup. Some may accumulate on the surface, in the form of scum or paint spills, and then pile up near the shore.'

An excellent site with questions and answers is found at:

Cyanobacteria do not pose a direct health risk as such, but they can produce toxins that have significant health effects. Some of these toxins are covered by the regulation on the quality of drinking water in Quebec. Certain bodies of water in Quebec, such as Missisquoi Bay of Lake Champlain, periodically have very high concentrations of toxins which represent high risks for drinking water consumption and contact water sports. Additionally, accumulations of cyanobacteria produce compounds that impart undesirable tastes and odors to water. These taste and odor compounds have no health effects but are unpleasant for the consumer.


Detecting and reporting cyanobacterial blooms in Lake Gervais

The Lac-Tremblant-Nord communiqué mentions that it is important to be vigilant and report accumulations of cyanobacteria. Due to the reports at lacs Tremblant and Bibitte, it would be useful to report any accumulation in Lac Gervais. When you are on the lake, you can easily make this observation.

What does an accumulation or bloom of cyanobacteria look like? Accumulations can be local, limited to the shore, concentrated in a bay (often downwind) or even present throughout the water column. They are found in the form of long streaks, scattered flakes or more or less homogeneous dispersions of the density of pea soup.

examples of blooms September 2023

If you observe such an accumulation and suspect the presence of a bloom, you can report this situation:

  • by completing the visual observation form and sending it by fax or email to the regional office of the Ministère de l'Environnement;

  • by calling the regional department of the Ministère de l'Environnement and asking to speak to the person responsible for the cyanobacteria reporting

  • outside opening hours, by contacting Urgence-Environnement at 1 866 694-5454.

Take photos and locate the site where you observed this accumulation. It would also be useful to notify the APLG so that this information can be shared.


Are cyanobacteria present and are blooms likely to occur in Lake Gervais?

Yes, there are cyanobacteria in Lake Gervais but at low concentrations, as in all lakes.. this is normal and a good sign.

Have we ever measured cyanobacteria in Lake Gervais? In 2022, we measured the presence of cyanobacteria by measuring phycocyanin, a pigment specific to freshwater cyanobacteria. Measurements taken on two dates at 5 points across the lake were below the detection limit of the probe. We were also enrolled in the Adopt a Lake program at the University of Montreal for toxin detection. Our samples did not have enough cyanobacteria to be able to detect them. We do not have measurements in 2023 but there have been no observations suggesting the presence of cyanobacteria blooms, unlike in Lakes Bibitte and Tremblant.

Are we at risk of cyanobacterial blooms at Lake Gervais? Several factors favor cyanobacteria blooms as summarized by the Quebec Ministry of the Environment: 'Several factors favor the proliferation of blue-green algae, such as high water temperature, weak current, water stagnation and climate change. The main culprit, however, is excess phosphorus.'

For phosphorus: We measured phosphorus in 2022 during characterization studies (see document section). This year we are participating in the RSVL program through which phosphorus was measured three times in 2023. The 2022 results show values ​​that classify Lake Gervais as ultra-oligotrophic, to oligotrophic with phosphorus concentrations similar to those of Lake Tremblant or Lake Joly. We are at low risk for phosphorus. For temperature: The water temperature of the lake warms up quickly, like that of all lakes in Quebec. The period of ice cover is decreasing rapidly in Quebec. These changes are important and increase the risk of cyanobacteria growth For climate change: intense rains that are becoming more and more frequent due to climate change increase the risk of blooms. Intense runoff brings more nutrients to the lakes (nitrogen and phosphorus), unless erosion is minimized. For Lake Gervais, this means that the riparian protection strips at the edge of the lake and tributary streams are really important to minimize this impact. Also important is the control of erosion and runoff during any construction. This pulse of nutrients during intense rains can trigger blooms a few weeks later.

Considering the 2022 data, Lake Gervais is exected to be a low-risk lake for blooms, like lakes Tremblant and Bibitte. And yet these lakes appear to be affected this year by blooms, which prompted the towns of LTN and Mont Tremblant to issue preventive advisories. Recent scientific publications suggest that northern lakes previously rarely affected (low in phosphorus) in Ontario and Sweden could be subject to blooms due to shorter periods of ice coverage and episodes of heavy precipitation. Future climate conditions may increase the Lake Gervais' vulnerability to blooms.

A comprehensive study was carried out by the University of Montreal, Polytechnique Montréal and HEC from 2016 to 2023. This major project called ATTRAP made it possible to advance knowledge on the prediction and control of cyanobacteria. Two residents of Lake Gervais, Julie Philibert and Michèle Prévost, took part in this major project. We developed monitoring tools, bloom prediction models and drinking water treatment methods.

Among the important findings of this major project that are relevant to our lake residents:

  • monitoring of cyanobacteria and their toxins can be done with tools that are easy to use and provide rapid responses (less than an hour). If a bloom was suspected at Lake Gervais, these tools could be available and useful.

  • treatment by filtration or UV does not remove cyanobacteria toxins. To remove toxins more advanced treatments are required such as ozonation, advanced oxidation and membrane filtration. Residents using Lake Gervais water without treatment or with only filtration + UV treatment could be exposed to cyanobacteria toxins, if there were any during the bloom.

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