Additional Instances of Deadly Whirling Disease in Fish Caused by Parasites Discovered in British Columbia’s Waters

The British Columbia government has reported additional cases of a parasite that Parks Canada warns could be highly damaging to young trout and salmon.

The provincial Ministry of Water, Land and Resource Stewardship has confirmed that three trout samples from the southern arm of Kootenay Lake have tested positive for the parasite responsible for whirling disease.

The first instance of this parasite in B.C. waters was discovered in September 2023 in Yoho National Park’s Emerald Lake, leading to the closure of nearby waterways while officials worked to contain its spread.

Authorities are uncertain if the new cases in Kootenay Lake are connected to Yoho National Park and are currently conducting further tests on samples collected this year as part of an ongoing investigation.

Kootenay Lake is recognized as one of the largest freshwater fisheries in the province, supporting Gerrard rainbow trout and kokanee populations that attract anglers from all over North America to British Columbia.

In May, the Canadian Food Inspection Agency designated the Columbia River watershed as an infected area for whirling disease following the initial detection of the parasite there in December 2023, leading to restrictions on the movement of fish—alive or dead—to and from other water bodies.

When the whirling disease was detected at Emerald Lake, Parks Canada warned that it could “decimate” up to 90 percent of young trout and salmon populations.

Although the parasite does not pose any danger to humans, authorities speculate that it may have been transmitted to B.C. from Alberta through human activities.

There are currently no known treatments for this disease.

The province advises individuals using B.C. waterways to follow the “clean, drain, dry” protocol for all boats and equipment coming into contact with river and lake water to prevent further spread, and to avoid moving fish from one body of water to another.