What’s killing the fish in Okanagan Lake?

by Dave Preston

With temperatures hovering in the mid-30s, the perfect end to the work week Friday night for the Allison family was a boat ride and some tubing on Okanagan Lake. Fun and a cool breeze were on the agenda, but the hundreds of dead fish they saw were a big surprise.

On a boat ride from Peachland’s 14th Street dock south, the odd silver, dead fish can be seen floating belly up. Not far off shore and just off 13th Street, ribbons of greenish-brown muck float on the surface. The more of the substance on the surface that can be seen, the more dead fish appear.

Several hundred metres off shore from the Peachland Castle, a large patch of the muck, about 10 metres by five metres, floats like a sheet on the lake surface. In the vicinity, scores of dead fish can be seen.

“I wasn’t sure if I should call someone or what,” said Steve Allison.

In total, a 20-minute boat ride revealed dead fish likely in the hundreds floating a few hundred metres off shore.

Though the Allison’s discovery was made on Friday the 13th, it’s not terribly unusual, according to a well known outdoors expert.

“It happens,” said Al Springer, long time member of the Peachland Sportsmen’s Association.

Springer said the dead fish are Kokanee and the muck is an algae bloom.

An algae bloom is a rapid accumulation of algae in an aquatic system and Springer said they have happened on Okanagan Lake in the past, killing hundreds, if not thousands, of fish.

Springer said hot weather seems to bring on algae blooms but added, “They don’t know what else we put in the lake that might be doing this.”

“People didn’t notice it (algae blooms on Okanagan Lake) years before,” said Springer.

The outdoorsman may be right. At the end of May, CBC News ran a report about the strange disappearance of Kokanee from Wood Lake in Lake Country. That report has gone viral on the web and describes a massive fish kill linked to algae.

Blooms occur when there is more than a normal nutrient load in a body of water, particularly phosphates, which can be found in fertilizers and some cleaning compounds containing phosphorous.

Algae is short lived and dies. When it decomposes, it deprives water of oxygen and that can lead to fish kills.

In the CBC report, provincial fisheries biologist Paul Askey said of the Wood Lake situation, “The Kokanee would prefer not to be in water that is 20 degrees and above up in the warm layers —and they couldn’t go down to the cooler waters because all the oxygen had been depleted by decomposing algae.”

The temperature of Okanagan Lake reached 20 C earlier this month and has been above that mark since July 10, according to data recorded on the Government of Canada’s Water Office website.