Manitoba

Parks Canada says it's not feasible to eradicate zebra mussels from Clear Lake

Fourteen months after live zebra mussels were found in Clear Lake in Manitoba, Parks Canada says it's not feasible to eradicate the invasive species from the largest body of water in Riding Mountain National Park.

Determination made following input from scientists, Indigenous advisers

A hand holding zebra mussels is pictured.
Parks Canada says it's not feasible to eradicate zebra mussels from Clear Lake in Riding Mountain National Park. Live mussels were first found in the park in November 2023. (Austin Grabish/CBC)

Fourteen months after live zebra mussels were found in Clear Lake, Parks Canada says it's not feasible to eradicate the invasive species from the largest body of water in Riding Mountain National Park.

Parks Canada announced Tuesday it made the determination after seeking input and advice from leading scientific experts, Indigenous advisers and officials with the province of Manitoba.

Adult zebra mussels were first found in the western Manitoba lake in November 2023. An effort to contain them within an underwater curtain at the Boat Cove area near Wasagaming during the summer of 2024 did not succeed.

Then in fall 2024, hundreds of live juvenile zebra mussels were found attached to docks and other structures near the east end of Clear Lake, Parks Canada said.

"This indicated that zebra mussels are not isolated to the Boat Cove area of the lake, where they had previously been found and where the containment curtain had been installed," Parks Canada said in an information bulletin.

In a followup email to CBC News, a Parks Canada spokesperson said eradicating zebra mussels requires the entire population to be identified, 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," the spokesperson said.

An attempt was made to isolate part of the lake where environmental DNA indicated the presence of a potential zebra mussel colony, the spokesperson said, but "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 acted "based on the best data available at any given moment since the first discovery of zebra mussel eDNA in the lake," the spokesperson said.

"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."

Trying to prevent spread

Parks Canada will continue to monitor water quality in Clear Lake and determine how to manage the lake now that zebra mussels are established in it.

The federal agency also said it will continue to try to prevent other invasive species — including black algae, spiny water fleas and rusty crayfish — from entering Clear Lake.

It also said it will try to prevent the spread of zebra mussels from Clear Lake to other bodies of water.

Zebra mussels were first found in Manitoba in Lake Winnipeg in 2013 and have since been found in Cedar Lake, Lake Manitoba and other bodies of water.

Zebra mussels have been eradicated successfully with the use of potash in a handful of small bodies of water on this continent, according to Invasive Mussel Collaborative, an organization of U.S. states, Canadian provinces, Indigenous nations and other public bodies. 

Those small bodies of water include a quarry in Virginia in 2006 and several harbours in a small lake southwest of Minneapolis in 2014, the Invasive Mussel Collaborative says on its website.

Watercraft will be allowed

The discovery of zebra mussels prompted Parks Canada to ban watercraft from Clear Lake in the summer of 2024.

On Tuesday, the agency said it plans to allow watercraft on Clear Lake on a "one boat, one lake" basis, similar to what it did in 2023.

Mike Moyes, Manitoba's minister of environment and climate change, says the province will do everything it can to minimize the spread of aquatic invasive species, but adds everyone has to play a role.

"We need Manitobans to come on board and work together with government, and that includes being responsible with their watercraft," he said.

"I would encourage all Manitobans to ensure that when they are in the water in the summertime … that they are cleaning, that they're draining and that they're drying their watercraft to ensure that we're not spreading aquatic invasive species."

With files from Bartley Kives and Cory Funk