In the fall, biologists counted only 2,000 kokanee in Wood Lake near Kelowna, 10 times fewer salmon than were counted two years ago.
"Wood Lake is our best kokanee fishery in B.C.,” said provincial fish biologist Paul Askey. “It's disappointing to see numbers that low."
He says Wood Lake is very rich in nutrients and that, coupled with a very hot summer in 2011, is likely to blame.
"The situation in the lake was pretty extreme for kokanee. Any water below eight to 10 metres had no oxygen, so the fish can't live down there. And anything above that depth was very warm, above 20 C, which is really warm for kokanee,” Askey said.
“Those conditions in the lake in 2011 were so extreme that they caused a significant mortality event and it seems they impacted all the age groups of fish that were in the lake at that time.”
He says water conditions in the lake improved last summer, and conservation groups are working to improve flows in the creek where kokanee spawn.
Askey says there should be enough fry to help the population recover by 2015.