Manitoba premier urges feds to keep Clear Lake open to boats after zebra mussels found last year

Premier Wab Kinew is urging Parks Canada to not ban boats at Clear Lake this summer after live zebra mussels were found at the lake late last year.

A letter sent from Parks Canada to Riding Mountain National Park business owners earlier this year, which was obtained by CBC, says it is considering options to prevent the spread of the invasive species in the western Manitoba national park — including the possibility of closing the lake to all watercraft.

"Clear Lake is a really, really important site for our province, and it's a hugely popular summertime destination," Kinew told CBC News earlier Tuesday.

"We're concerned that the federal government appears to have taken a unilateral decision here, so we're making the case to them to hold off and to keep Clear Lake open."

In an email to CBC News, a Parks Canada spokesperson said "no decisions about the management of the lake have been made at this time."

The letter sent to business owners, dated Jan. 26, 2024, says if the watercraft ban option is followed, outside beach toys would also be banned, but those items would be provided at no cost through a lending program.

The letter also lists two other options for the lake's use. One would provide an exemption for watercraft that do not leave the lake for any period of time.

The other option would allow the use of self-propelled vessels like canoes, or closed floatation equipment like paddleboards and catamarans, as well as non-inflatable beach toys.

Parks Canada officials found live zebra mussels in Clear Lake at Boat Cove in Riding Mountain National Park last November, the agency's website says.

Since then, it's conducted sets of water sample tests, including one set between Jan. 8 and Feb, 2, and another between Feb. 2 and Feb. 20. 

Though both sets of tests came up negative for zebra mussel environmental DNA, Parks Canada's website says the invasive species could still be present in the lake.

"A potential infestation of zebra mussels in Clear Lake presents a real threat of significant and irreversible ecological damage to the lake and downstream waterbodies," its website says.

Results from Feb. 20 to March 8 water samples are expected in the next few days, the Parks Canada spokesperson said. In total, 73 per cent of the lake has been sampled.

The federal agency has engaged in broad consultation, the spokesperson said, which included First Nations leaders and elders, other levels of government, representatives from the tourism industry and other businesses, environmental groups, and people who use the lake.

The Opposition Progressive Conservatives called on the NDP government to act immediately to protect Clear Lake, including adding more boat inspection stations and working with Parks Canada to prevent zebra mussels from flowing into downstream tributaries.

Jamie Moses, the province's minister responsible for natural resources, said during question period at the legislature Tuesday that the government's latest budget includes an additional $500,000 to fight the spread of aquatic invasive species and increase watercraft inspection and decontamination stations.

Potash treatment 'effective': scientist

Kinew's Tuesday plea comes after Parks Canada drafted a detailed impact assessment report in February 2024, which was emailed to CBC News from a Riding Mountain National Park spokesperson.

According to the report, the federal government is considering how it could eradicate the invasive species from the lake, including the use of potash molluscicide, a chemical registered for pesticide use in open bodies of water in Canada.

The report says Parks Canada could use the chemical in small, isolated parts of the lake. It could also use physical control methods, including manually removing the mussels or using benthic mats — thick large tarps anchored to the bottom of the lake used to smother and kill the mussels. 

The report says Parks Canada could also use a combination of these methods.

Scott Higgins, a research scientist with the Experimental Lakes Area, said that's exactly what Parks Canada would need to do, but the challenge is making sure they don't miss any areas.

"Clear Lake's a big lake," Higgins told CBC News. "You're gonna need to do this in a lot of areas."

Zebra mussels are highly sensitive to potash, or potassium chloride, even at low levels, and the chemical is highly likely to eradicate the animals in the areas that it treats, said Higgins.

It was also used to kill zebra mussels in Lake Winnipeg in 2014, albeit with mixed results.

"It was very effective at killing the mussels within the harbours, but unfortunately zebra mussels had already established in the main lake outside of the harbours," he said.

"So shortly after the treatments, the zebra mussels simply just recolonized."

The chemical is widely used in agriculture and has minimal impacts on human health. It also doesn't seem to affect other aquatic species, other than freshwater mussels, which zebra mussels tend to eradicate anyway, said Higgins.

"It's one of the most effective tools," he said.

If Parks Canada does decide to use potash in the lake, it would need to cordon off areas where the mussels tend to cluster, like rocks or the sides of docks, with plastic curtains held down at the bottom of the lake. The benthic mats could also be used to cover softer areas of the lake's floor.

"Essentially you're isolating a volume of water in parts of the lake where you think the zebra mussels are," said Higgins.

If Parks Canada does decide to use potash, it should do so before the lake warms up and the mussels start reproducing, he said.

"The mussels probably aren't very active and they're not reproducing until water temperatures exceed about 10 to 12 degrees Celsius" — which is why there still could be mussels in the lake despite the negative water sample tests, Higgins said.