Koocanusa algae bloom kills thousands of salmon

Thousands of dead fish found floating on the surface near the Canada-US border.

  • Sep. 9, 2013 5:00 a.m.

Two weeks ago there was a mass die-off of Kokanee Salmon in Lake Koocanusa. Thousands of fish floated on the surface near the Canada-US border.

Area B Director Heath Slee brought up the subject at the Regional District of East Kootenay meeting Friday, Sept. 6.

“Some of the local people complained that they saw all these carcasses of kokanee salmon floating upside down on the lake and in the reservoir,” Slee said. That was the first thing he’s heard about it happening two weeks ago.

He found that Montana Fish, Wildlife and Parks biologists attributed the die-off to a blue-green algae bloom.

The kokanee, 8-10 inches in size, came to the surface because of the long stretch of hot, dry weather this summer on Koocanusa.

“The two-year-old salmon came up to feed on this algae, which they typically do, and once they ingest this algae, it affects their bladder and so they are not able to dive down into the cooler waters again,”

he said, adding that unless they can reach those cooler depths, they cannot thrive.

“So consequently there was a huge die-off. It hasn’t affected the over-species, from what I’ve been told, it’s not harmful, it’s not going to affect the wildlife,” Slee said, adding that if you’re out there fishing and catching salmon there’s also no concern about eating the salmon.

Slee said it has happened before and biologists believe it is the algae that caused it.

The salmon would be becoming mature and spawning in the fall of 2014, so it may have an effect on future stock.

“Unfortunately a lot of those salmon have died,” Slee said. “I don’t know what the end result will be or how it will affect the salmon fishery next summer, but it has been a major die-off at this stage and it has hurt in the past.”

According to an article in the Tobacco Valley News, Montana biologist Mike Hensley estimated that 10,000 juvenile kokanee were dead as a result of the algae bloom.

Slee said he hadn’t heard of any local biologists looking into the situation, but said they were probably aware of the die-off.

The kokanee were introduced into Koocanusa a number of years ago and this year’s salmon will begin spawning in the creeks and rivers in the next few weeks.