Thousands of dead fish have surfaced in three Central Alberta ponds and lakes because of winterkill.
© Rory O’Connor
Thousands of dead fish have surfaced in three Central Alberta ponds and lakes because of winterkill.
Thousands of dead fish have surfaced in three Central Alberta ponds and lakes because of winterkill.

In Crimson Lake, thousands of perch died and collected around the shoreline.

While not pleasant for lake visitors to look at or smell, winterkill is a natural phenomenon.

"They're very common in Alberta," said Jessica Reilly, senior fisheries biologist out of Alberta Environment and Parks Rocky Mountain House office.

In Central Alberta, winterkill was also reported at Dickson Trout Pond and Pine Lake.

"Basically what happens is the plants and algae in the lake over winter die and decompose. When they decompose they use up oxygen."

The longer the decomposition, the more oxygen is used up. That is exacerbated in a long winter because oxygen can't be replenished while the water is covered by ice.

Some lakes in Alberta are hit by winterkill every year. It is more hit and miss at Crimson Lake.

Reilly said nature has its own way of cleaning up the mess. Birds and various weasel species enjoy the floating buffet of dead fish.

Eventually, the fish decompose and sink to the bottom where they provide food to various invertebrates, such as dragonfly and fly larvae, which are in turn eaten by fish.

How badly winterkill hit Crimson Lake's perch population - which tends to be resilient - has not yet been determined.

"We'll have to go out later in the season, in the next couple of months, to assess whether it's a partial or complete kill."

The province has not stocked Crimson Lake since the 1950s. At one time, perch and trout were put in every year. But that stopped because of repeated winterkills.

How the perch that fell victim to this year's winterkill got into Crimson Lake is a bit of a mystery. Once thought wiped out by repeated winterkills decades ago, perch were detected about five years ago.

They were possibly introduced illegally, or the hardy perch population may have slowly recovered on its own.

"We're not totally sure where the perch came from in Crimson Lake, but it was definitely not a planned fishery," said Reilly.

While nature will clean the lake on its own, not all local residents are willing to wait that long. Alberta Environment and Parks has approved licences to community groups who plan to scoop the fish and dispose of them at the landfill.

Reilly said the province does not mind people cleaning up dead fish, but a licence is required. Signs have been posted at the lake reminding residents.