Whirling disease needs constant vigilance, Montana fish expert says after Banff lake becomes Canada's 1st case

Officials must stay on top of dealing with whirling disease in affected fish in Banff, says an American expert who have been dealing with the problem since the 1950s.

The first known Canadian case of whirling disease was found in Johnson Lake in Banff National Park, which is now closed to the public.

The disease is caused by a microscopic parasite that affects trout and salmon, and can cause infected fish to swim in a whirling pattern and die prematurely.

"[In] the Madison River, we saw a 90 per cent decline in juvenile rainbow trout," said Eileen Ryce, hatchery bureau chief for Montana Fish, Wildlife and Parks, referring to an outbreak in the mid-1990s.

"By the time we had … figured out the cause of [the] mortality, it had spread to several rivers. And now we have it in a lot of our trout areas throughout the state," Ryce told the Calgary Eyeopener on Friday.

The parasite eats the fish cartilage, which causes internal damage, deformities and mortality in very young fish that have more cartilage than hard skeleton, Ryce said from Helena.

"We put our hatcheries on clean water, and that will really help limit the spread," she said, adding that officials still test the hatcheries annually to make sure they are clean.

They also stress the message "clean, drain, dry" to members of the public, especially anglers, who can spread the parasite via their boots or boats.

While Montana's fisheries were severely impacted in the early '90s, it's not all bad news.

"The fishing industry rebounded pretty quickly.… The fish have developed their own resistance, they're using different areas for spawning, and in some cases we did have changes in population structure to more resistant species, like brown trout," Ryce said.

"But our fishing is just as good as it's always been, some may say better in some areas," she added.

Parks Canada has closed off the Johnson Lake area, east of Banff, for recreational use after officials confirmed the first Canadian case of whirling disease in the fish there on Thursday.

Fish from other bodies of water in Banff National Park are being tested and Alberta Environment and Parks is sampling fish downstream from the park.

Whirling Disease is not harmful to humans or other mammals.

Suspected cases should be reported to 1-855-336-BOAT.

With files from the Calgary Eyeopener