On the Frontlines of Stopping Zebra Mussels

In an average summer, Clear Lake, Manitoba, is a relatively peaceful place. But in the summer of 2024 the quiet is striking. Across this placid expanse of water in the heart of Riding Mountain National Park, you can still hear a loon's call, a swallow's chatter, the splash of a waterfowl lifting off for the far shore. Other familiar sounds, though, are absent. No outboard motors, no water skiers carving wakes, no shouts and music and laughter drifting across the lake.

This summer, recreational boating here has been banned. Clear Lake has become the new western battlefront in the war against the zebra mussel.

Invasive species are a global problem. Forests, meadows, lakes, waterways and cityscapes around the world are being transformed by newcomers brought by human activity to places where no natural predators exist and local species are vulnerable. Ecologists in Riding Mountain National Park keep watch for nasty aliens like the spiny water flea and Eurasian water milfoil.

But few invaders are feared like the zebra mussel. Native to the Black and Caspian sea regions, they multiply at a nightmarish rate, potentially achieving a density of up to 10,000 per square metre. A shopping cart recently pulled from infected Lake Winnipeg was reportedly unrecognizable as anything other than a monstrous mussel metropolis.

The resulting problems range from clogged water intake pipes to toxic algae blooms and decimated fish populations. A single zebra mussel can filter a litre of water per day. En masse, they consume huge amounts of the phytoplankton that support other species. “There's some documentation out east that fish populations have decreased 50 to 70 per cent five to 10 years after the arrival of zebra mussels,” says Tim Town, Riding Mountain National Park's lead ecologist.

Since their takeover of the Great Lakes in the late 1980s, the mussels' westward progress has been inexorable. Lake Manitoba, the massive body of water only a 90-minute drive east of the national park, fell prey to an infestation three years ago. So far Clear Lake marks the western Canadian boundary of the spread, although in the United States, zebras and the closely related quagga mussels have been found in both Nevada and California.

In 2017 the discovery of zebra mussels in Montana led to the establishment of new monitoring stations and a doubling of inspectors in the Okanagan water basin.

B.C. too is on the alert.

The first indication of zebra mussels at Clear Lake came from a sample taken in August 2022. Last year, more evidence was discovered at a boat launch area in this beloved tourist destination about an hour north of Brandon. After months of discussion, the decision was made to keep boats off the lake this year. In a town where the seasonal economy is 100 per cent tourist-driven, that is no small thing.

Dameon Wall, external relations manager at the national park, points out that zebra mussel larvae (called veligers) have limited mobility. “They don't swim,” he says. “They drift on the current. They don't hitch rides on ducks or beavers. It's human activity — they arrive on boats.”

Which is why boaters and float plane owners are urged to clean, drain and dry their crafts and store them out of water for extended lengths of time, as zebra mussels can’t survive more than 30 days out of water.

The drama playing out in Clear Lake this summer is a natural detective story, involving DNA analysis and desperate attempts to preserve the chain of evidence. Finding the culprits is a matter of not simply seeing their ominous striped shells on docks, rocks and pipes, but picking up their telltale genetic markers in the water. Nor is the boat ban merely about preventing further contamination — it's also about managing the crime scene. Boats cruising the lake are equivalent to crowds tracking back and forth over a bloody chalk outline. “Boats moving all over the place confound the sampling process,” Wall says.

Water samples are analyzed for environmental DNA (known as eDNA), which can indicate the presence of sperm, excretions or even larvae. Town points out that eDNA can survive on boats and in bilge water even if the boats have been decontaminated. Decontaminated boats won't be spreading larvae, but they could spread confusion.

“If a boat were to release some [contaminated] bilge water at the north end of the lake,” says Town, “and it happened to coincide with our sampling, now we have eDNA at the north end of the lake, which makes detection that much more complex.” (Zebra mussel DNA recently discovered in nearby Whirlpool Lake was eventually determined to have come from bilge wash.)

Park staff are now preparing to move into attack mode. A sort of silk curtain will be placed around the boat launch area in late July, and the enclosed waters treated with potash. It's not toxic to fish but kills zebra mussels.

Wasagaming, the town that nestles the southeast shores of Clear Lake, is a postcard-ready vacation spot, relatively unchanged for decades. Aside from some big long-weekend crowds, it has a relaxed feel that seems to date from the era before mass travel. Still, Riding Mountain National Park draws over 300,000 visitors a year, and local businesses are entirely dependent on them. A boating closure was bound to cause alarm. “We knew some people would be happy and others less than happy,” says Wall.

How unhappy? There was reportedly talk among some merchants about a lawsuit to stop the federal government from enforcing the boat ban. According to George Hartlen of the Wasagaming Chamber of Commerce, the talk went nowhere. “There were definitely discussions,” he says. “People are concerned about change, and there's always talk about extremes. But I think it was just a lack of understanding.”

Hartlen points out that Clear Lake is at the top of a watershed, connecting to the Little Saskatchewan River and thence to the Assiniboine that runs through Brandon and on to the Red River. “Communities downstream have a stake, too,” he says.

Wall says the pushback wasn't too bad. “What's become clear is the amount of support there is to protect the waters of Clear Lake,” he says. “There's a very strong desire to see a healthy lake.”

“We did hear a lot of concerns about the impact of having no opportunity to have an on-the-water experience here,” Wall says. “So there are some exemptions.” One is a large lake cruiser called the Martese. “It still operates and provides lake access to thousands of people. We can work with the operator of that vessel and in essence set his path for him, whereas if there were hundreds of boats going all over they would be impossible to track.”

A closure such as Clear Lake’s does provide an intriguing opportunity to study the environmental impacts of human activity. Just as the COVID travel freeze (and the 9/11 crisis before it) offered climate scientists a chance to gauge the effects of jet emissions on weather, could the abrupt cessation of boat traffic lead to revelations about changes in activity by marine birds and wildlife? The verdict is still out.

“We do have sites to measure water quality,” Town says. “Time will tell. As well, there were some waterfowl surveys conducted from 1999 to 2001. We're going to replicate some of those methods over the summer and see what bird species are coming back. But it's too early.”

It's also too early to gauge the effects on tourist numbers. But anecdotal evidence suggests the effect of the boat ban has been negligible. “The streets are packed on weekends,” says Hartlen, “and there are lineups at the ice cream shops. The biggest impact is always the weather. It's miserable weather that keeps people away.”

The relative peace and quiet this summer has even led to discussions about whether a boat ban might be extended, zebra mussels or no. The number of boaters is a small fraction of overall visitor totals — fewer than 1,000 permits were issued in 2023. One local merchant even suggested that the lack of boating may have drawn visitors to restaurants and businesses instead, silencing critics of the ban. “Once they saw the restaurants were full,” he says, “they stopped complaining.”

Jet Skis have been banned here for years. But Wall insists a permanent boat ban is not coming. “There's at least 100 years of established boat use on this lake,” he says. “These are temporary measures. Nobody is talking about this being the end of boating.”

Meanwhile the invaders keep coming. While the national park has always had plenty of wood ticks, the black-legged deer ticks that carry Lyme disease are now being found in the eastern regions of the park. Some Alberta waters have been infected with the parasite that causes whirling disease in salmonid fish species.

And the zebra mussels? Despite the efforts of Town and other park staff, they persist. Last week the national park issued an update: “On July 17, 2024, while conducting a visual survey, Parks Canada snorkellers found a partial shell and one living, adult-sized zebra mussel attached to a rock. Water samples collected from Boat Cove from June 19 to 27, 2024, have also tested positive for environmental DNA from zebra mussels. This evidence shows the invasive zebra mussels are building a presence in Clear Lake.”

“The changes in environment that we're seeing now, it's like a two-pronged attack,” Wall says. “Invasive species benefit from climate change to move into new zones. They are part and parcel of the same problem. Multiple vectors are at play to disturb the natural systems that have been established here.”

And the frontlines in these battles are moving west.