Officials have started pulling all the fish from Johnson Lake in Banff National Park where the deadly fish parasite that causes whirling disease was first detected in Canada, in a bid to stop its spread.

The disease predominantly affects trout and whitefish and can cause them to swim in a whirling pattern and die prematurely.

Officials with Parks Canada will use netting and electro-fishing to remove the fish from the 15-hectare lake. 

Parks Canada says it's confident removing the fish will be effective, because of the lake's location and the fact it is relatively small in size and shallow in depth. 

Whirling disease was first detected in Canada when it was found in Johnson Lake in August 2016, but has since been detected in the entire Bow River and watershed and the Oldman River basin in Alberta.

The ambitious measure at Johnson Lake is the best strategy to try to stop the disease from spreading into nearby Two Jack Lake and Lake Minnewanka, says Banff National Park resource conservation manager Bill Hunt.

"There's only 10 core populations in all of Banff National Park for westslope cutthroat [trout]," he said.

"These are some of the last pure strains of westslope anywhere in the world, and so protecting those and making sure that we do as much as we can reasonably from being severely impacted by whirling disease is a pretty high priority."

Hunt says because of the whirling disease, the fish will be euthanized and disposed of safely.

Disease spreading

The disease is caused by the microscopic parasite Myxobolus cerebralis.

Infected fish can also exhibit skeletal deformities and their tails can turn a darker colour, even black.

The disease is not harmful to humans and the CFIA said there are no health concerns for people using the infected bodies of water or eating infected fish.

Hunt said he expects Johnson Lake will be restocked in a couple of years if the project proves to be successful.