Mass die off of fish in Island lake in Ontario, Canada

Winterkill

Unusually thick ice is taking the blame for an above average winterkill of fish at Island Lake.

As the manmade body of water continues to melt, numerous visitors to the conservation area have reported spotting large amounts of dead fish surfacing on the lake.

According to Credit Valley Conservation (CVC), thick ice cover on the lake deprived fish of oxygen leading to their death.

Ice acts as a barrier between water and the air. Fish and decaying plants will consume oxygen available in the water eventually leading to suffocation. Winterkill is common in shallow lakes and ponds.

The water in Island Lake is about four feet deep. This winter, ice on the lake exceeded two feet in depth.

“We had unusually high depths of ice,” said Wayne White, chairman of the Friends of Island Lake. “It’s just an act of nature. It has nothing to do with water quality or anything else.”

Island Lake bass have suffered the brunt of the winterkill, according to White.

“The pike can survive on lower levels of oxygen,” he said.

Dead fish will usually surface in concentrated numbers where ice first begins to melt. White said dead fish sightings in the lake are being reported near Bob’s Bridges. However, the new boardwalk is not to blame for any aquatic casualties.

“It was quite a shock to people walking across Bob’s Bridges and seeing the fish there,” White said. “It was the first area for the ice to melt on the lake.”

CVC has implemented voluntary trial harvest limits on fishing at the lake.

Bill Lidster, CVC’s senior superintendent of conservation areas, said the limitation aims to allow the lake to replenish its own fish population.

“We’re confident with those trial harvest limits the lake will replenish itself,” Lidster said.

Although dead fish sightings may be gruesome, Lidster explained the overall percentage of fish that are dead is likely low.

“This is just a natural occurrence,” he said.

White added the fish fatalities wouldn’t have an impact on Friends of Island Lake’s fishing derby scheduled for early July.

CVC staff also plan to keep an eye on fish species that experience winterkill and the extent of any die-offs.

“We don’t want people to all of a sudden not register and think they won’t catch fish,” White said.

CVC is warning of the possibility of an increased winterkill throughout the entire Credit River watershed.

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