How whirling disease in B.C. could threaten a lucrative fishery

Marie Veillard stands at the edge of the vast Kootenay River in Kootenay National Park. She's checking on a group of fry, baby fish she's been looking after for a few weeks now.

They're happy to see her, aggressively swimming for the food she's feeding them in their cage on the river — part of a Parks Canada monitoring program to detect early signs of the disease. 

As the rain falls on the gin-clear water, Veillard, a Parks Canada aquatic invasive species expert, remembers the moment she saw a group of fry chaotically swirling around her feet in the nearby Crowsnest River in Alberta. 

A stark contrast from these happy fish and a tell-tale sign of whirling disease, it's not a moment she says she will soon forget as she embarks on a quest to stop the deadly condition from spreading across B.C., where it was found for the first time last year.

The microscopic parasite that causes the disease preys on young fish, causing them to swim in a whirling pattern, and often eventually killing them. It has the potential to wipe out entire fish populations, causing lengthy closures that could devastate economies that rely on fishing and fish tourism.

Veillard is concerned because once the disease is present, it's nearly impossible to get rid of. 

"Normally, when you walk into the water, you might see a fish, but it will scurry away really quickly. In this case, these fish weren't able to escape. They weren't able to swim away from us, and it was really heartbreaking," said Veillard.

Whirling disease was first detected in Canada in Johnson Lake in Banff National Park, Alta., in 2016. 

It has since been found in some of Alberta's major drainage basins and watersheds, including the Crowsnest, South Saskatchewan, Red Deer, and North Saskatchewan rivers and, last year, made its way to B.C.

In December 2023, the Canadian Food Inspection Agency confirmed the presence of whirling disease in Yoho National Park. It has been found in the Kicking Horse River, part of the Columbia River Watershed.

Veillard says the disease originated in Europe and made its way to hatcheries in the United States in the 1950s through the aquaculture trade. 

In the 1990s, it was discovered in wild systems in the U.S., and since then, near-total collapses of some trout populations have been observed in Colorado and Montana.

In response, Parks Canada has closed all water bodies to watercraft and fishing in both Yoho and Kootenay National parks until at least March 31, 2025. 

Veillard says it's a necessary measure to slow the spread of the debilitating disease. And it allows time and space for researchers like her to better understand its patterns.