Zebra Mussel Information and Updates

Zebra mussels (Dreissena polymorpha) are native to eastern Europe. They were first detected in North America in the Great Lakes in the mid-1980s. Since then, they have infested many waterbodies in eastern North America. They were first detected in Manitoba in 2013 when they were discovered in the south basin of Lake Winnipeg. They later also colonized the Red River from the US border to Lake Winnipeg. Since then, they have invaded the Nelson River from Lake Winnipeg to Hudson Bay, as well as Cedar Lake and Lake Manitoba.

Biology

Zebra mussels are freshwater hinged mollusks. They are filter feeders that attach themselves to solid surfaces. They breed very quickly, as females can release up to one million eggs each breeding season. After the eggs are fertilized, larvae (called veligers) emerge and are free-floating for up to a month. The larvae are microscopic and do not swim. Veligers float through lake and river currents until they settle on a solid surface. This natural dispersal method means they can easily affect waterways downstream from an invaded area. Zebra mussels have few, if any, natural predators in North America. As a result, they often permanently alter the food web and ecosystems they invade.

Negative impacts on people include:

• Increased maintenance costs
• Damage to equipment such as boats, hydro-electric generating facilities, water intakes, and other infrastructure along infested water bodies
• Injury from sharp shells
• Potential negative health impacts resulting from increased likelihood of toxic algae blooms

Negative impacts on aquatic ecosystems:

• Altering the food web by out-competing native species, like native mussels and other small invertebrates, for food (plankton)
• Removing large amounts of non-toxic algae (plankton) from the water and leaving behind toxic algae (cyanobacteria) to thrive, causing toxic algae blooms
• Affecting fish spawning areas by changing the surfaces of rocks and vegetation, impacting the survival of fish eggs
• Creating clearer water, allowing sunlight to penetrate deeper and changing the habitat by increasing the growth of submerged aquatic vegetation

Zebra mussels are especially harmful to native mussels, many of which are species at risk. They outcompete these species for food and will attach themselves to native mussels, suffocating them.

An infestation of zebra mussels in Clear Lake presents a real threat of significant and irreversible damage to the lake and downstream waterbodies.

Summer 2011 – Monitoring for AIS, specifically zebra mussels, in Clear Lake begins.

Summer 2015 – Mandatory Parks Canada AIS inspections and decontaminations begin at Riding Mountain National Park.

Summer 2011 to 2023 – Water samples from Clear Lake and surrounding water bodies are taken and tested for zebra mussel eDNA.

January 2023 – Parks Canada is informed by Fisheries and Oceans Canada of a positive test result for zebra mussel eDNA in a water sample taken at an area known as Boat Cove, in Clear Lake on August 4, 2022.

May 4, 2023 – Parks Canada announces that trailered watercraft intended for use on Clear Lake must not have been in any other waterbody in 2023 and must undergo an inspection by June 15. Boats that met the requirements had a tag installed that sealed the boat to the trailer. This tag ensured that the watercraft had not been in another waterbody and posed no risk of bringing in aquatic invasive species. If this tag was removed or tampered with, the boat would not be allowed to launch in Clear Lake for the remainer of the 2023 season. All human-propelled vessels (canoes, kayaks, stand-up paddle boards) were required to undergo a Parks Canada AIS inspection, and if needed, decontamination before launching in park waters.

November 10, 2023 – Parks Canada officials do a physical search at Boat Cove and a clump of 48 live zebra mussels was found and removed from the water. Before that, zebra mussels had never been found in Riding Mountain National Park.

May 2024 – Parks Canada implements watercraft management measures that restricted all recreational watercraft use on Clear Lake for the time required to determine if a population of zebra mussels had been established and for any potential remediation. With exceptions for emergency vessels, the commercial tour boat The Martese, and one vessel from the Keeseekoowenin Ojibway First Nation.

August 2024 – Parks Canada closes the Boat Cove for the construction and installation of an impermeable containment curtain in Clear Lake. The curtain was installed in an area of the lake where living zebra mussels were found in November 2023 and July 2024. Shortly after installation, the curtain was damaged and was no longer an effective means of containment and would be removed. The curtain could not be repaired or replaced.

September 2024 - Parks Canada found hundreds of living juvenile zebra mussels attached to docks and infrastructure near the east end of Clear Lake.

October to December 2024 - Extensive internal and external review of the evidence and data collected from Clear Lake in 2024.

With the exception of 2024, recreational motorized boating has been permitted via Superintendent’s Order on Clear Lake for many years. Non-motorized boating is permitted on all waterbodies in Riding Mountain National Park. All watercrafts must undergo and pass a Parks Canada AIS inspection prior to launching.

Historically, only electric motors, four-stroke engines, and direct fuel injection two-stroke engines have been permitted on Clear Lake, along with human and wind-powered watercraft.

In 2025, Parks Canada plans to allow watercraft on Clear Lake under a "one boat, one lake" aquatic invasive species prevention program. The program, similar to the one in 2023, would likely involve a tagging system to ensure that vessels have not been in other water bodies and do not pose a risk of introducing new aquatic invasive species into Clear Lake.

The specifics of the 2025 program, including the types of watercraft it will apply to and the implementation details, will be determined based on public input and available resources. Parks Canada will invite the public to provide feedback on how the program should be applied.

Parks Canada is seeking input from stakeholders, visitors, and community members to determine the best long-term approach for the "one-boat, one-lake" program. This input will be considered in management decisions to ensure the program reflects the values of all parties involved.

Details about the prevention program for Clear Lake in 2025 will be widely communicated before season opening (May Long Weekend).

Human-powered watercraft will be permitted on outlying waterbodies under a re-evaluated aquatic invasive species prevention program. The public will be invited to provide input into how the 2025 program will be applied.

The key principle behind “one boat, one lake” is that it minimizes the movement of invasive species from lake to lake. Aquatic invasive species can be transported through water on boats, trailers, or even in mud on the equipment. If people are committed to using their boats only on one water body, it reduces the risk of transporting invasive species.

As part of broader aquatic invasive species prevention efforts, this program also stresses the importance of boat inspections and following Clean, Drain, Dry principles. This includes draining all water, removing mud and vegetation, and drying the watercraft and all related equipment thoroughly between launches.

Parks Canada representatives will be set-up near the skating rink behind the Visitor Centre on February 1 and 2 from 12:00 PM to 4:00 PM. The information collected will be used to inform the management of Clear Lake’s aquatic invasive species prevention program for 2025. There is also an opportunity to provide input through an online questionnaire available until February 28, 2025 through this link: https://parks-parcs.simplesurvey.com/f/s/Clear-Lake-Riding-Mountain-2024

A review of data in the fall of 2024, with input from Indigenous advisors, the Province of Manitoba, and leading scientific and international experts determined that eradication of zebra mussels from Clear Lake is no longer an achievable option.

Eradication requires that the full population be identified, fully isolated and contained from the rest of the lake. There was significant time and effort spent trying to find a population cluster, as well as preparing for eradication attempts if such a population was found.

Although an attempt was made to isolate an area of the lake were eDNA had indicated the presence of a potential colony, additional data gathered in 2024 demonstrated that zebra mussels are much more spread out in the lake than initially thought, and the full extent of the zebra population is not yet known. Parks Canada has taken action based on the best data available at any given moment since the first discovery of zebra mussel eDNA in the lake.

At the end of the boating season, zebra mussels were detected at numerous, widespread locations in the east end of the lake. Based on size, growth rates and numbers found, establishment likely occurred earlier in the summer, before the curtain was installed. Even if the curtain had held up, zebra mussels would not have been fully contained and eradication would not have been successful.

The containment attempt was based on the best available information and was initiated in the area with the highest potential for zebra mussel establishment. The failure of the curtain was something that demonstrated the limits to using this approach to isolate sections of large, open bodies of water.

Understanding why high rates of eDNA were detected in Boat Cove and lower rates of eDNA were detected where other living populations of zebra mussels have since been found requires further analysis.

Over time, zebra mussels are likely to spread throughout Clear Lake and downstream. Although veligers cannot actively “swim”, they will be spread by natural currents (e.g. thermal cycling, wind driven, and gravity). Zebra mussels are likely to negatively impact the existing ecology of Clear Lake by altering food chains, water quality and aquatic habitats. There may be a greater risk for toxic blue-green algae blooms which pose increased risks to visitor safety.

Zebra mussel veligers float through lake and river currents until they settle on a solid surface. Although they are likely to spread downstream through the outlet of Clear Lake, via Wasamin Creek (Clear Creek), down through the Little Saskatchewan and Assiniboine River Systems, it is currently unknown exactly how far they may travel and whether they will reach suitable habitat to settle and reproduce.

Aquatic invasive species monitoring will continue and will be focused on the spread of zebra mussels throughout the western portion of Clear Lake. There will be an increase in monitoring and sampling at outlying lakes such as Moon Lake, Grayling Lake, Whirlpool Lake, Lake Katherine, Lake Audy, and Deep Lake. Ensuring that zebra mussels are not spread to other lakes in the surrounding area will be considered imperative.

Parks Canada will monitor infrastructure throughout Clear Lake and assess management options while evaluating the establishment of the zebra mussels. There are no immediate concerns about the implications for water treatment infrastructure. Park staff will monitor this infrastructure and water quality and will continue to provide potable water into the future.

If evidence of zebra mussels is found in another waterbody in Riding Mountain National Park, Parks Canada will take similar steps to further investigate and assess potential containment and eradication options.