Whirling disease infects entire Bow River basin

A world-class trout fishery, the Bow River is now infected with whirling disease.

The Canadian Food Inspection Agency has advised that the entire Bow River watershed in southern Alberta has been contaminated by the contagious disease. That includes all feeder streams and lakes such as the Elbow River and extends all the way down to where the Bow joins the South Saskatchewan River.

The provincial government is testing other rivers to see if it has turned up elsewhere and has ordered a “precautionary quarantine” of fish farms and hatcheries. That remains in place until they test their stock and it shows negative.

While not a risk to humans wading in the water or eating infected fish, the parasite can kill small, young fish. Mortality rates in vulnerable populations have been as high as 90 per cent.

In Alberta, the most susceptible species are rainbow, westslope, cutthroat and brook trout, as well as mountain whitefish. Symptoms include swimming in a circular pattern, a change in colour and skeletal deformities as the disease eats away at cartilage.

“It impacts them in terms of how they’re able to respond to their environment,” said biologist Lorne Fitch, a former adjunct professor at the University of Calgary. “They do actually start to twist and turn because they can’t align themselves anymore. There’s not an awful lot that can be done about it.”

Alberta Environment spokesman Peter Giamberardino said there’s no indication the infection has affected trout stocks in the Bow and the province has no plans to change fishing regulations in the river.

The province will monitor for the disease at watercraft inspection stations and boaters are asked to help prevent its spread by cleaning, draining and drying their boats and all equipment when moving between bodies of water.