Zebra mussels testing in Manitoba's Clear Lake could trigger potash treatment response

Parks Canada is racing against the clock in their fight against zebra mussels in Riding Mountain National Park after the discovery of a live adult specimen.

"Zebra mussels are building a presence in Clear Lake. Riding Mountain National Park staff are moving forward with efforts to contain the area, with the goal of preventing the spread and preparing for a potential eradication attempt," agency spokesperson Dameon Wall said in a virtual media briefing Wednesday.

Every year, zebra mussels cause millions of dollars in damage in Canada by clogging intake structures in power stations and water treatment plants and by damaging boats. They also compete with native species for resources.

Parks Canada snorkellers found one adult zebra mussel and a partial shell in Boat Cove in Clear Lake last week.

Since then, scientists have sent 78 water samples to the Department of Fisheries and Oceans from different parts of the lake, including the marina, east end boat launch, North Shore cottages and western campsites. They hope to get the results by next week.

If the invasion is still isolated, Wall said they will install an impermeable curtain in the water starting Monday. Studies done in smaller water bodies have found success with this containment method for mussels and their larvae, known as veligers, he said. 

Then, they'll decide whether to treat that area with potash, a pesticide which was approved by Health Canada in 2022 to eradicate zebra mussels. Tim Town, the ecologist team leader, said there are no known negative effects on other wildlife or people drinking from the lake.
    
"I think it's prudent just to wait until the next round of samples come in, just to ensure that we do have an isolated population, which we're assuming that we do, based on our current testing results that we received," Town said.

"We are preparing for potential treatment. We do have a contractor lined up to come as soon as possible if a treatment is triggered."

However, if testing shows mussels are already establishing in other parts of the lake, "then the likelihood of a treatment goes down considerably. It would not be prudent to treat the whole lake," Wall said.

Clear Lake was closed to most outside watercraft this season, after scientists found live zebra mussels in the lake in November. Recreational boats such as canoes, kayaks and paddleboards, are not permitted.

Two people have been charged under the Canada National Parks Act for paddleboarding on the lake during the closure, according to a Parks Canada statement. The charges could result in fines up to $25,000 each. However, "that's not telling us where these mussels may have originated," Wall said Wednesday.

All of this worries those living and working in the park.

"There's nothing more heartbreaking than seeing what's happening," said Karly McRae, president of Lakehouse Properties and chair of the local destination enrichment organization, Clear Lake Country.

Some bookings are down 10-20 per cent, cancellations are up, "and I think most of it is due to the messaging out there that Clear Lake is closed. That's not true. Clear Lake is open for business and continues to be a great place to visit."

Residents and business owners are hoping Parks Canada will hold public community meetings so they can ask questions and get some answers.

It's been difficult to hear news first in the media, McRae said.

"I think it's important to share that information with the community first ... so that we can better understand what they're facing, what their approach is going to be to a long-term plan in dealing with aquatic invasive species," she said.

"We are really interested in being part of the solution and in working together to solve this complex problem and to make a plan for the future."