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Routine maintenance at Whitehorse dam last fall ends with hundreds of dead fish
The large metal fish screens that block one of four turbines, part of the Whitehorse dam. (Yukon Energy)
Low water prompted ‘rapid dewatering of sensitive areas,’ consultant’s report states
At least 761 fish died last year below the Whitehorse dam while Yukon Energy was doing maintenance work related to protecting fish.
According to a consultant’s report done for Yukon Energy, and obtained by CBC News through an access to information request, the fish were killed last October when the company caused water levels below the dam to drop too low.
“The 2024 event resulted in fishing stranding at levels that were much higher than previous years where monitoring occurred,” states the report by Environmental Dynamics, a consultancy firm with a branch in Whitehorse.
The report states that the fish killed included 447 slimy sculpin, an indicator species of cold water quality, as well as 172 juvenile Arctic grayling and 133 longnose suckers. One juvenile chinook salmon died.
The maintenance work done over two days in early October involved crews removing fish screens — used to prevent chinook salmon from entering one of four turbines — and the steel beams that hold them in place, before the river freezes. The large metal screens cannot stay in after a freeze-up or they could damage the system.
To make for safe working conditions, Yukon Energy drew water levels down by about a metre each day in some areas for a few hours. The consultant’s report said that “led to a rapid dewatering of sensitive areas” below the dam.
An exceptionally high Yukon River last year coupled with limited storage in Schwatka Lake affected Yukon Energy’s ability to reduce flows slowly. The result is that flow rates had to be reduced more quickly than in previous years, causing a more rapid water level change.
A spokesperson with the Department of Fisheries and Oceans declined to comment, saying an investigation into the issue is ongoing.
Company taking steps ‘to avoid that happening again’
Kirsten Hogan, a member of Yukon Energy’s technical working group for the dam, said the company is working to protect fish and the ecosystems they’re part of.
“The results in 2024 were not something that anyone was expecting to see, and that’s why there has been so much concerted effort to both understand why that happened the way that it did, and how we can take steps to avoid that happening again,” she said.
Changes include using fish salvage teams only as a last ditch effort to get stranded fish back into the water.
Perhaps the most salient, though, is the company’s plan to slowly reduce flows.
“It gives fish the opportunity to notice that there’s changing water levels and to move out of those areas,” Hogan said. “And that’s something that they do naturally when water levels drop in the fall. So we’re trying to be as close to that kind of natural fish behaviour as possible so that they have the opportunity to not get stranded.”
A Yukon Energy spokesperson told CBC News the company has implemented this change in its ramping protocol. Ramping is the rate at which Yukon Energy changes river flows.
Hogan said Yukon Energy has also surveyed more sensitive areas that could be prone to stranding. That includes upstream of the dam.
“We’ve improved our understanding of the shoreline, so we now have much more detailed information on potential stranding spots and those are the spots we’ll be monitoring when we’re testing that protocol,” she said.
Mechanizing the feat of removing the fish screens each fall — for example, by using a lift — is another possible change.
“This year, the situation is very different,” Hogan said.
“We’ve had lower water levels. Inflows are already starting to drop.
“We also recognize the importance of those fish to, particularly to the First Nations in the Whitehorse area, and to the overall ecosystem. And we know the importance of doing everything we can for those fish.”
