This story originally appeared in the Spring 2025 edition of Salmon Steward, the Pacific Salmon Foundation’s quarterly print magazine.
A parasitic disease that can be lethal for juvenile salmon has been recently detected in British Columbia.
Whirling disease – named after the erratic spinning behaviour of infected fish – was first detected in Canada in 2016 in Alberta.
In December 2023, whirling disease was first detected in B.C. at Emerald Lake in Yoho National Park. A year later, it was found in Kootenay Lake, a vital habitat for kokanee sockeye salmon.
In extreme cases in the western U.S., whirling disease has resulted in fish populations collapsing by more than 90 per cent. There is currently no known treatment.
Whirling disease often leads to blackened or deformed tails and skull deformities in fish. While there is no threat to human health, activities like swimming, boating, and fishing are catalysts for introducing the disease to new areas.
To stop the spread of whirling disease, the Province of B.C. is leading campaigns to encourage cleaning, draining, and drying all boats or equipment when transferring between water bodies. Recent regulation changes have also made it illegal to transport a boat with the drain plug still in place as undrained boats can spread larval or microscopic invasive species.
In April 2025, Parks Canada announced that all waterbodies in Yoho and Kootenay National Parks will be closed to anglers and boaters until at least March 2026 due to the continued presence of whirling disease.
Surveillance of invasive mussels
Another looming threat to salmon in B.C. comes from invasive mussels.
Zebra and quagga mussels, originally from Europe, found a home in the Great Lakes in the 1980s. Since then, they’ve spread west, hitching a ride in the ballast water of boats, trailers, and equipment.
These shellfish have established in eastern Canada, but have also been found in western U.S. states. Concerningly, quagga mussels were recently discovered in Idaho – which connects to the Pacific Northwest through the Columbia River system.
“For 10 years, the Government of British Columbia has been working with our many partners to support the Invasive Mussel Defence Program, a vital effort to protect our waterways and communities,” says Hon. Randene Neill, Minister of Water, Land and Resource Stewardship. “We’re committed to stepping up enforcement at the borders, which represent the highest risk of entry into our province, including developing better regulatory tools. These collective measures will also help reduce the spread of whirling disease in our waterways.”
Threat to salmon
The mussels have not yet been detected in B.C., but to mitigate the spread, PSF contributed $50,000 to the Province of B.C.’s Invasive Mussel Defence Program in 2024.
“The establishment of invasive zebra and quagga mussels in British Columbia could be devastating for Pacific salmon. It would become a top threat for salmon populations and their habitats,” says Jason Hwang, Chief Programs Officer and Vice President, Salmon at the Pacific Salmon Foundation. “We need to be proactive in surveillance efforts at entry points into the province to prevent invasive mussels from establishing in British Columbia and wreaking havoc on local ecosystems.”
Invasive zebra and quagga mussels disrupt aquatic ecosystems in several ways. They aggressively filter water, depleting essential food sources like plankton and contribute to the growth of toxic algal blooms. Furthermore, the establishment of large mussel colonies in salmon habitats can disrupt spawning and threaten egg survival.
The province has already seen close calls. In 2023, the B.C. Invasive Mussel Defence Program intercepted 155 high-risk watercrafts entering the province. Of those, 79 were decontaminated and 36 were quarantined. 14 were confirmed to carry invasive mussels.
PSF continues to work closely with the Province of B.C. to mitigate these threats to salmon and their habitat.
For further information, visit the Province of B.C.’s website for details on whirling disease and invasive mussels. You can also contact WhirlingDisease@gov.bc.ca about whirling disease and COS.Aquatic.Invasive.Species@gov.bc.ca about invasive mussels.
