Researchers say all the fish in British Columbia’s Emerald Lake may need to be “culled” after the discovery of a rare parasite in the water.
But first more tests need to be done.
Parks Canada says it is investigating a suspected case of whirlpool disease in Yoho National Park’s Emerald Lake.
The disease is a microscopic parasite that affects trout and salmon, and can cause infected fish to swim in a vortex and die prematurely.
The agency says this is the first time the parasite that causes the disease has been detected in the province.
Shelley Humphries, an aquatic ecologist with Parks Canada, said the agency has been on high alert since the disease was discovered in a lake in Banff in 2016.
The current round of testing was prompted by the discovery of a deformed brook trout caught by Parks Canada staff in late August.
Humphries said fish samples from the lake were sent to a laboratory to check for the presence of the disease, and results received Tuesday indicated it was likely present.
But, he said, it is considered a “suspicious case” and more sampling will be necessary to confirm the presence of whirling disease.
The lake and connected waters are closed for testing
Meanwhile, Emerald Lake, Emerald River, Peaceful Pond and One Duck Lake, along with their shorelines and tributaries, are closed to swimming and boating, although surrounding trails will remain open.
Parks Canada says all watercraft, water-related equipment and angling are prohibited and fines for violations can reach up to $25,000.
“We want to make sure that if this is really positive… park visitors don’t accidentally infect [the disease] somewhere else,” Humphries said.
Parks Canada said young fish, such as rainbow and brook trout, are especially susceptible to eddy disease, with a mortality rate of about 90 per cent.
The disease does not pose any risk to humans.
Humphries said it will be several weeks before enough samples can be collected and analyzed.
Sacrifice some fish to save others: biologist
If whirlpool disease is confirmed, it could have a devastating impact.
Once established, researchers say, it is impossible to eradicate the parasite, which is a known invasive aquatic species.
In August 2016, the first known Canadian case of whirling disease was detected in Johnson Lake in Banff National Park. In an effort to stop the spread of the parasite, officials began removing fish from the lake and eventually all of them had to be killed.
José Álava, a senior researcher at the University of British Columbia’s ocean pollution research unit, said that will likely be the outcome at Emerald Lake as well.
“The best thing they can do is harvest all the fish and basically cull them,” he said.
Álava said killing the fish, which include salmon and rainbow trout, will have a major impact on fishermen and indigenous groups in the area, but the alternative is for the disease to spread further.
He explained that after the fish die prematurely, the parasite spores remain in the environment and contaminate the water sediments.