Last September, a suspected case of whirling disease prompted Parks Canada to shut down several lakes in Yoho National Park, B.C., including Emerald Lake. The agency recently confirmed the presence of the disease in Emerald Lake, with further spread observed in the Kootenay River watershed.

According to the Canadian Food Inspection Agency, whirling disease is a contagious infection which affects finfish. Infected species may display signs such as a whirling swimming pattern; skeletal deformities, such as shortening of the mandible and indentations on the top of the head; and a dark or blackened tail. The infection, which has previously proved devastating to fish populations, currently has no treatment. Transmitted through contact between finfish and a freshwater worm (Tubifex tubifex), the potential impact of whirling disease is severe, with mortality rates reaching up to 90 per cent in some cases.

Speaking with CBC News, Robyn Hooper, executive director of the Columbia Shuswap Invasive Species Society, said, “The impacts of whirling disease in infected waters can cause high mortality in fish populations… Juvenile fish are the most susceptible to infection.”

Hooper also urged boaters to remain on high alert. While humans cannot contract the disease, it can be spread by individuals through the movement of infected live or dead finfish, infected worms, contaminated equipment, or contaminated water. Cleaning, draining, and drying all watercraft and fishing gear is a crucial step in preventing the spread of the disease.

During a recent news conference, Francois Masse, Parks Canada’s field unit superintendent for Lake Louise, Yoho, and Kootenay national parks, said “Aquatic invasive species, such as the parasite responsible for whirling disease, threaten freshwater ecosystems and native trout populations, harm infrastructure and reduce aquatic recreational opportunities.”

In emphasizing the severity of the situation, he added, “Once established, aquatic invasive species may never go away.”

Although whirling disease has previously been found in Alberta, the Yoho National Park cases mark the first confirmed cases of whirling disease in B.C. As a precautionary measure, Parks Canada closed all bodies of water and shorelines in Yoho National Park and Kootenay National Park last October. The closures are set to remain in effect until the end of March.