Officials are considering removing fish from Johnson Lake near Banff in an effort to stop whirling disease from spreading to the nearby Two Jack Lake and Lake Minnewanka.
The entire Bow River Watershed — which includes Johnson Lake — is infected with the disease that mainly affects trout and whitefish, causing them to swim in a circular pattern before dying prematurely.
Lake Minnewanka and Two Jack Lake are part of the Upper Cascade area and testing has shown the disease has not spread to those waters.
"The Minnewanka system is connected, it's fed by the Upper Cascade, and that's one of the areas in Banff that has two or three of our critical habitat areas for westslope cutthroat trout," said Bill Hunt, resource conservation manager for Banff National Park.
"We're very concerned about preventing whirling disease from getting into Minnewanka and the Upper Cascade. We have Sawback Lake, Sawback Creek, Cuthead Creek — are all critical habitat for westslope cutthroat trout."