CALGARY — Parks Canada officials and some of its contractors were on Johnson Lake Tuesday checking a series of gill nets and scaring ducks away from them.

It’s part of a multi-year project to remove all fish that are susceptible to whirling disease.

The first Canadian case of the disease was found at Johnson Lake in August 2016.

Bill Hunt, the resource conservation manager for Parks Canada in Banff National Park, said the lake was stocked with brook and rainbow trout, but as they’ve been cleaning the lake, they have found a lot of brown trout as well.

“It indicates quite possibly somebody dumped fish into this lake unlawfully and that may be where whirling disease came from,” said Hunt.

According to Trout Unlimited Canada, whirling disease affects salmonid fish (trout, char, whitefish, salmon) and can cause very high mortality rates.

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.

Whirling disease was first described in Europe over 100 years ago and was introduced to North America over 50 years ago. Since then, whirling disease has been implicated in severe population declines of wild trout in many water bodies across the continent.

Hunt said it’s important to protect the native trout further up stream in the national park, which has some of Alberta’s only populations of westslope cutthroat trout.

“We’ve done a lot of work to restore genetic purity up there. We’ve done reintroduction, removals of rainbow trout and it’s really critical to save those headwater populations because they then influence everything downstream.”

Johnson Lake is a popular winter recreation site for skaters but Parks Canada says the ice surface will be too dangerous this winter because as the lake continues to drain, it compromises the covering ice.

Because of that the lake will remain closed to the public this winter.

The fish cull and draining of the lake should be completed by spring or summer of 2020.