Zebra mussels
A constant vigilance, forever !
Zebra mussels in our lake and surrounding region
The discovery of zebra mussels in Lake Memphremagog in 2017 led to strengthened monitoring and preventive measures in Lake Massawippi. Thanks to these efforts, the arrival of this invasive species was delayed by more than four years, and its early detection in 2021 revealed a still small and vulnerable population.
In 2022, Bleu Massawippi ramped up its initiatives to protect the lake. Seven volunteers were trained to support professionals. Together, they carried out 262 dives—over 700 hours underwater—removing 18,727 zebra mussels. Research showed that the mussels were mostly concentrated in the northern part of the lake, with densities still relatively low.
Other important measures included boat washing and the study of larvae to better understand their spread. The success of these actions is the result of collaboration between Bleu Massawippi, the community, and local authorities, who worked together to intensify control efforts in 2023. Acting together is essential to protect the ecosystem, preserve lake activities, and avoid significant financial consequences.
In 2024, we observed relatively low population densities, we however witnessed a slow population growth that indicates the importance of maintaining our controlling efforts.
Density survey using quadrats, conducted in November 2022. At each station, 16 quadrats of 0.25 m² were randomly deployed and inspected — 8 at a depth of 2 meters and 8 at 6 meters. The approximate average density was 0.2 individuals/m².
Quadrats survey
The quadrat survey protocol, developed in collaboration with the MELCCFP, allows for monitoring and quantifying zebra mussel populations in a lake. Scientific divers inspect pre-established stations and assess environments conducive to their colonization.
In 2022, 21 stations were studied around Lake Massawippi. This was adjusted to 18 stations in 2023 and 2024. After three seasons of surveying, we continue to observe higher numbers of zebra mussels in the northern half of the lake. A few mussels have been found in the southern portion, suggesting they have not yet firmly established themselves in that area. However, it is important to recognize the detection limits of this methodology.
After three field seasons, average zebra mussel densities remain low compared to other lakes in the region. The density observed during the last season indicates a slowed population growth, which can be attributed to removal efforts since 2021.
Overall, control efforts appear effective but would benefit from improved detection of heavily colonized areas. The mussel population continues to grow and mature in parallel with the actions taken by Bleu Massawippi and its partners. While Bleu Massawippi continues to explore technological approaches to increase control efficiency, shoreline residents and lake users are encouraged to remain vigilant and support efforts to preserve the lake’s ecosystem.
Summary of the analysis of pyramidal substrates deployed in Lake Massawippi in 2022.
The small collector substrates are simple, user-friendly devices suspended from docks in shallow water. They offer shoreline residents a chance to take part in data collection and help protect their lake. While these devices have a lower detection capacity than the pyramidal substrates, their combined use provides a broader picture of zebra mussel spread.
In 2022, 12 pyramidal substrates and 47 small citizen substrates were deployed in Lake Massawippi, with the help of 37 shoreline residents. An additional 30 small substrates were installed in nearby rivers and Lake Lyster. All devices were inspected from July to October to assess zebra mussel presence.
Substrates
At Lake Massawippi, two friendly and collaborative methods are used to monitor the spread of zebra mussels, an invasive species: pyramidal substrates and small substrates.
Pyramidal substrates are clever devices made of PVC plates, submerged 2 meters below the surface. Zebra mussel larvae, called veligers, attach to them and grow over time. The substrates are retrieved and inspected at the end of each field season. This method allows for tracking zebra mussel development and comparing different areas and lakes.
Distribution and Summary of Small Collector Substrates Upstream and Downstream of Lake Massawippi, in 2022
Some closely located points are difficult to distinguish due to the scale used. Zebra mussel counts ranged from 1 to 3 on the 5 positive substrates.
Spatio-temporal estimations of veliger concentration in lake Massawippi, 2024
Veliger monitoring
The veliger sampling protocol, developed in collaboration with Fisheries and Oceans Canada, allows for monitoring microscopic zebra mussel larvae in Lake Massawippi. This method helps anticipate the arrival of new mussels, even though a direct link between veligers and the location of juvenile mussels cannot be firmly established.
In 2022, samples were collected regularly throughout the lake. Veligers were present as early as May, when water temperatures began to rise, peaking in June, and gradually declining until November. The spatial distribution of veligers remains unclear due to significant variability (or "noise") in the sampling results.
A comparison of veliger densities between October 2021 and 2022 shows a decrease. However, it is not possible to determine whether this drop is due to control efforts or environmental factors. The peak veliger concentrations observed in Lake Massawippi remain significantly lower than those recorded in Lake Memphremagog.
Without continued control measures, Lake Massawippi could experience a similar rise in veliger concentrations. Lake users must remain vigilant and continue collaborating to safeguard biodiversity and water quality.
Summary of zebra mussel removal dives conducted by Bleu Massawippi in 2022.
Left: Overview of the entire lake.
Top: Zoom-in on the area where most dives were concentrated.
Center: Close-up of the water intake zone.
Mussel removal dives
The Bleu Massawippi team dedicated significant effort to monitoring the zebra mussel population in Lake Massawippi, completing 262 dives in 2022. Divers explored the lakebed—where zebra mussels tend to concentrate—using a geo-referenced mobile app and inflatable markers to analyze mussel densities across different stations and over time.
In 2022, 18,727 zebra mussels were removed, mainly from the northern part of the lake. This number is significantly higher than in 2021, reflecting improved operational efficiency. The support of the community and partners—such as Plongée Magog, the Aquarium du Québec, and the Montréal Biodôme—was essential in the fight against this invasive species.
Bleu Massawippi is also working to train volunteer divers to strengthen control efforts. In 2022, 7 volunteer divers were trained. The team also inspected water intakes in North Hatley and Waterville, where zebra mussels were found. These municipalities could benefit from a monitoring and pipe-cleaning strategy.
Together, shoreline residents, lake users, and partners can help preserve this beautiful environment and maintain the relaxing atmosphere of Lake Massawippi.
North Hatley boat washing station
In 2022, Bleu Massawippi collaborated with the Village of North Hatley to improve its watercraft washing service, which is essential in the fight against zebra mussels and other invasive species. The mobile washing station operated daily from April 22 to October 31, with operating hours ranging from 12 to 15 hours per day depending on the season.
Washing watercraft remains crucial to prevent the introduction of new larvae or other invasive species, even though zebra mussels are already present in Lake Massawippi. Thanks to this collaboration, 2,612 watercraft were washed—setting a record for the boat launch.
The increase in non-motorized watercraft, such as kayaks, canoes, and paddleboards, presents new challenges. While the risk of transmission per vessel is lower, the growing number of watercraft increases the overall risk. It is therefore important to raise awareness among lake users about the need to protect this ecosystem.
Bleu Massawippi is also considering the possibility of making exit washing mandatory to prevent Lake Massawippi from becoming a source of zebra mussel spread to other lakes.
Trash removal
The Aquarium of Québec and Mission 1000 Tonnes partnered to carry out a pilot underwater cleanup project near the Federal Wharf of Lake Massawippi, in North Hatley. In a single friendly day, 10 divers managed to collect 883 pounds of waste, including 185 zebra mussels that were attached to the debris—demonstrating the dual positive impact of this initiative for the lake.
The Aquarium of Québec expressed its enthusiasm in supporting Bleu Massawippi for future cleanup operations in 2023. Thanks to this collaboration, shoreline residents and lake users will benefit from a healthier environment, while also helping to curb the spread of zebra mussels and preserve the water quality and ecosystem of Lake Massawippi.
This joint effort helps create a relaxing and enjoyable atmosphere for everyone who loves the lake, emphasizing the importance of protecting this beautiful natural setting for future generations.
Active search for zebra mussels in 2020
Presented by Vincent Lemieux, Project manager at Blue Massawippi
STOP MZ printemps-été 2025
Moule zébrées
In 2025, the fight against zebra mussels continues. After a summer of intensive removal efforts in the northern part of the lake and a few dives in the south, we counted a total of 87,862 mussels collected. Thanks to 400 hours of research in a single summer, we can conclude that our efforts are continuing to slow the spread of zebra mussels, with density still relatively low compared to the expected population growth curve. These results encourage us to maximize our efforts for improved monitoring and control of the zebra mussel population in Lake Massawippi. To learn more, check out our latest density study here!
Don’t forget your critical role in eradicating these invasive populations—starting with regular boat washing, raising awareness among your peers, and consulting the many resources available on our website.
