What’s killing fish in Okanagan Lake? Province says viral outbreak, weather changes may be cause

Thermal shock or disease could be factors into a recent kokanee die-off in Okanagan lake that has some residents concerned.

“We headed out on the lake and noticed the kill off of these fish which [and] we were quite alarmed. It’s the first time we’ve seen in it in our 10 years of boating,” West Kelowna resident Scott Thresher said.

“There are about six-inch kokanee and they’re right across the lake, both sides and in masses and we’ve never seen it before.”

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    Thresher said he was boating on the lake near the West Kelowna Yacht Club when he saw hundreds of dead fish.

    “Of course you immediately think that the lake has been poisoned or something but then we realized that it was just this particular species of fish and nothing else was floating at the top,” Thresher said.

    The province said sudden changes in water temperature or a viral outbreak could be why more than 1,000 kokanee have washed up on the shores of the lake since Thursday.

    “While biologists have yet to pinpoint what is causing the kokanee deaths, previous die offs in Okanagan Lake and elsewhere have been associated with strong winds that can send warm surface water deeper into the lake,” public affairs officer for the Ministry of Forests, Lands and Natural Resource Operations, Greig Bethel said in a news release.

    One of the dead fish that washed up on the shore of Okanagan Lake.

    Dan Couch/Global News

    Bethel said tissue samples are being analyzed by staff at a fish health lab in Duncan  to find out if disease was a factor in the recent kokanee deaths.

    “Die-offs in other lakes have been linked to the infectious hematopoietic necrosis virus – IHNV,” he said.

    While the numbers of dead fish that are washing up on valley shores is alarming to some, Bethel said the die-off won’t have a large impact on the lake’s overall kokanee population.

    “Last year, biologists counted more than 336,500 spawning kokanee on the lake, the most since annual counts began in 1992,” he said.

    ~ With files from Blaine Gaffney