Whirling disease confirmed in B.C. for 1st time, sparking fears for fish populations

A debilitating parasite that causes a fatal disease in fish has been confirmed in British Columbia for the first time, four months after a suspected case in the Rockies caused several bodies of water to be closed.

Emerald Lake and several nearby lakes in B.C.'s Yoho National Park, roughly 175 kilometres northwest of Calgary, were shuttered after a suspected case of whirling disease was found last September.

Parks Canada said on Friday that further testing confirmed the presence of whirling disease in Emerald Lake. It also confirmed the disease had spread to bodies of water in the Kootenay River watershed.

"It's definitely very concerning," said Robyn Hooper, executive director of the Columbia Shuswap Invasive Species Society. "The impacts of whirling disease in infected waters can cause high mortality in fish populations … Juvenile fish are the most susceptible to infection."

Hooper urged boaters to clean, drain and dry all watercraft and fishing gear to prevent the spread of invasive species.

"That includes waders, life-jackets, kayaks — anything that can hold on to mud, water or fish — before moving between water bodies," she said.

The disease is caused by a microscopic parasite, which primarily targets trout and salmon. It causes infected fish to swim in a whirling pattern and, in the vast majority of cases, die prematurely.

A young trout is photographed with a deformed tail, a symptom of whirling disease, a parasitic condition that was officially confirmed for the first time in B.C. on Friday. (Submitted by Parks Canada)

'Significant threat' to parks' aquatic ecosystems

Parks Canada said in a statement that the disease poses a "significant threat to the health of national parks and their vital aquatic ecosystems."

The agency said this is the first time the parasite has been confirmed in B.C., but that it had been on high alert since the disease was found in a lake in Banff in 2016.

"Whirling disease has the potential to decimate fish populations, with mortality rates up to 90 per cent in some cases," the agency said.

As a precaution, Parks Canada closed all bodies of water and shorelines in Yoho National Park and Kootenay National Park last October. They will remain closed until the end of March.