Banff National Park officials begin fish cull in Johnson Lake

Using netting and electro-fishing, Parks Canada officials began eradicating fish from Johnson Lake near Banff this week in an effort to stop whirling disease from spreading to other bodies of water.

Electro-fishing is a non-lethal way of capturing fish, usually used for doing counts.

"Basically it's a backpack unit, you walk through a stream or a shallow portion of a lake," said Mark Taylor, an aquatic ecologist with Banff National Park.

• All the fish in this Banff lake are to be removed and killed to protect other lakes from whirling disease

"You've got an anode and a cathode in the water and you're creating an electric current around you. That electric current gives way to a very predictable behaviour in fish, where they're stunned so they come up to the surface, and often times they swim toward the electro-fisher."

Nets are then used to scoop up the stunned fish, then they will be killed.

Because they could be contaminated, they will be disposed of in an approved landfill.

Johnson Lake was the site of the first confirmed case of whirling disease in Canada, which was discovered last August but the disease has since been detected in the entire Bow River and watershed and the Oldman River basin in Alberta.

• Whirling disease now infects entire Oldman River basin, including Waterton Lakes National Park

Whirling disease is a parasite which affects salmon, trout, char and whitefish and causes them to swim in a whirling pattern until they die. Johnson Lake was stocked with brook and lake trout decades ago.

The goal of the eradication is to protect other bodies of water, namely the nearby Two Jack Lake Reservoir and Minnewanka Lake Reservoir, which are currently free of whirling disease.

"One of the streams that drains into the Minnewanka Reservoir is called the Upper Cascade, and it's home to several core populations of westslope cutthroat trout, they're listed as threatened," said resource conservation manager Bill Hunt.

To better protect those fish populations, access to Two Jack and Minnewanka was closed when whirling disease was detected.

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.

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