Fish kills in Okanagan Lake a mystery

An investigation is going on into two fish kills in Okanagan Lake, but it’s not yet known whether they are related or not.

Hundreds of dead carp and Northern pike minnows were discovered Monday in and around Rotary Marsh in Kelowna’s downtown north end, where Brandt Creek flushes into Okanagan Lake.

Conservation officer Ed Seitz was at the scene Monday afternoon and said he couldn’t see any evidence of a chemical or fuel spill, but he removed some of the carcasses to have some laboratory tests done on them.

All the fish he saw were coarse fish rather than game fish, and he said it appeared they died within the past day or two.

City of Kelowna staff have also taken water samples both in Rotary Marsh—a re-constructed wetland that is now a city park—and at several spots upstream in Brandt Creek, but there were no results by the Capital News deadline, according to Todd Cashin, Environment and Land Use manager with the city.

Cashin had visited the site earlier in the day and said there didn’t appear to be different age classes, but he couldn’t speculate what might have caused the deaths.

There was quite a rapid change in surface water temperatures in the past few days, he noted.

That is also being noted in relation to a kokanee fish kill in two sites in the main lake. A dozen or so dead kokanee were reported in the north end of the lake, and thousands in the south, with around a thousand discovered last week across from Peachland, according to stock assessment biologist Paul Askey with the Forest Land and Natural Resource Operations ministry in Penticton.

He wonders whether it’s disease-related, but in order to get the necessary lab tests done he needs a dying fish that is not yet dead on which to do them.

If you find a struggling kokanee that is not yet dead, call him immediately to report it, at 250-490-8200, so he can collect it.

There have been similar kokanee die-offs in the past in Okanagan Lake, often in July, but not since 2009. Sometimes the numbers have been in the hundreds of thousands, where this appears to have only affected a few thousand kokanee, Askey said.

He believes whatever the event was, it’s likely over now. It appears to have occurred between July 12 and 17.

There has been speculation during previous die-offs about the impact on water mixing because of windy conditions; on the impact of a particularly high spring freshet; or on the effect of sudden water temperature changes on the fishes’ physiology.

Two years ago there was a fish kill in Osoyoos Lake caused by the columnaris bacteria, which can be a factor when warming water stresses fish.

However, Okanagan Lake is much deeper and offers plenty of opportunity for fish to move down the water column to cooler water.

Askey noted there was a recent rapid change in surface water temperatures in Okanagan Lake.

Ministry biologist Tara White noted such large fish kills are not uncommon on large lakes, and most are still mysteries.

“One theory is that it has something to do with high winds and sudden lake turnover which is hard on the swim bladders and fish equilibrium,” she commented.


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