Lack of oxygen kills thousands of fish near Banff

Those taking in the views at a popular lake near Banff, Alta., will likely see a large amount of dead fish from the shore, according to Parks Canada. 

Fish in the second lake at Vermilion Lakes, directly west of Banff, recently died from winterkill said Mark Taylor, aquatic ecologist team lead in Banff National Park. Winterkill naturally happens when the fish don't get enough oxygen. 

He said Parks Canada became aware of the dead fish after a report came in from the public. 

Fisheries managers in Canada are well aware that winterkill happens at times, Taylor said. 

But it can be surprising when witnessed by the public. 

"There's a lot of people who like to spend time here because of the diversity of wildlife that are here, and we just want them to understand that when they see these dead fish that it is a natural event," he said. 

"As much as we love Mother Nature, unfortunately she's cruel sometimes." 

The lakes are home to native and non-native species. Taylor said most of the fish that have died are white suckers and brook stickleback, native species to Vermilion Lakes and Banff National Park 

Parks Canada is warning people to be vigilant about wildlife when they visit Vermilion Lakes, should they encounter any that come to the area to feed on the fish. 

Taylor said magpies and coyotes have already started showing interest in the area, but risk to the public is considered low "at this time." 

"Most of it is still covered up by ice, so it's going to certainly be on our radar for watching it as the season progresses and certainly by Spring," he said.

Parks Canada said winterkill happens often in shallow lakes when ice and snow levels above the water's surface become so thick that light can't penetrate the surface. 

Underwater plants and algae aren't able to produce oxygen due to the absence of light, which causes the fish to asphyxiate and die. 

Taylor said Parks Canada is aware that there were previous winterkills at Vermilion Lakes in 1959 and 1964.