Parks Canada closes B.C.'s Emerald Lake due to suspected case of whirling disease

Rainbow trout occupy a pond at Rushing Waters Fisheries, Tuesday, July 3, 2012 in Palmyra, Wis. (Wisconsin State Journal-John Hart/AP/THE CANADIAN PRESS)

Parks Canada says it is investigating a suspected case of whirling disease in Emerald Lake in B.C.'s Yoho National Park.

It marks the first time whirling disease has been detected in B.C., according to Parks Canada.

Whirling disease is harmless to humans, but can devastate fish populations if unchecked.

"Young fish (juvenile salmonids), such as rainbow trout and brook trout, are particularly susceptible to whirling disease, with mortality rates reaching up to 90 per cent," Parks Canada said in a release.

"Once established, whirling disease is nearly impossible to eradicate."

To contain the possible spread, Parks Canada has closed Emerald Lake, Emerald River, Peaceful Pond and Lone Duck Lake, along with shorelines and tributaries, to all members of the public until further notice.

Shelley Humphries, the aquatic specialist for Lake Louise, Yoho and Kootenay National Parks, said the test results came back late Tuesday afternoon from samples that were collected on Aug. 21.

"We had a few hits from a few fish that were sampled of a larger number of fish so we need to go back to do some additional testing just to confirm that it's really there and not some sort of artifact from the lab," she told CTV News Friday.

The closures have been put in place to prevent anyone from accidentally spreading whirling disease to other water bodies, she said.

"As of today we've closed lake for water activity like using your personal, stand up paddle board or angling just to provide as much protection to the park that we can."

The disease is caused by a microscopic parasite called Myxobolus cerebralis that requires two hosts: a Tubifex worm and a salmonid fish.

The parasite affects a fish's nerves and damages cartilage, which can cause the fish to swim in a whirling or tail-chasing behaviour.

"It can cause their populations to crash. Some fish are really dramatically affected," Humphries said.

"But we have to emphasize that this is absolutely not human issue – this is a fish disease and ecological integrity issue for the park."

'ACCIDENTALLY SPREAD'

Whirling disease has been accidentally spread throughout North America since it was introduced from Europe several decades ago.

That transmission comes most easily with the transport of infected fish and fish carcasses, but Humphries says the parasite can survive in the lake itself too.

"It can be found in the mud, in the plants or even the water. So if people leave with a dirty boat and go launch in another location, that's one of the suspected ways it's being transmitted around."

Humphries says people can also spread whirling disease by wading into one lake and then wading in another in the same day.

Nearly three years ago, conservation officers drained Banff National Park's Johnson Lake and removed all of its fish after Canada's first case of whirling disease was found there in 2016.

Humphries says Parks Canada's key strategy to prevent the spread of whirling disease has been communication with visitors.

"Since 2018, Parks Canada and Yoho National Park has been implementing a permitting system and communication around people, needing them to clean, drain and dry all of their equipment," she said.

"If people clean all obviously mud off their equipment, if they dry it and get rid of all the water and dry it for up to 48 hours, then they have very little chance of being able to transmit this or any other aquatic invasive species."

Anyone who violates the closure order can face a fine of up to $25,000.

(With files from Kevin Fleming)