Thousands of fish could be killed at Whitehorse dam, new study suggests

CBC

19-06-2025

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Thousands of fish may be killed as they swim downstream through the hydroelectric dam in Whitehorse, a new study suggests — and that's something one environmentalist is calling "unacceptable."
Prepared by the B.C.-based environmental consulting firm EcoFish under contract for Yukon Energy, the research is linked to the relicensing process for the dam, now in front of the Yukon Water Board.
EcoFish has studied fish mortality associated with the dam before. Its latest research, though, estimates the number of fish that could be killed.
The research, based on two years of field work as well as data going back several years, suggests that many fish are being unwittingly sucked into intakes such as the dam's four turbines — a phenomenon called entrainment.
An estimated 25,063 resident fish, which include whitefish, grayling and Northern pike, are entrained each year, the study states. More than half of those — about 15,470 — could be killed.
Then there are imperilled chinook salmon, with an estimated 43,000 to 203,000 juveniles entering the intakes annually, the study states. Between 13,000 and 62,000 of those will be killed, it says, representing about 30 per cent of all migrating juvenile salmon in the Yukon River.
This would mean that if 200,000 juvenile salmon were to move downstream, it's likely that less than one per cent of those would return as adults to the Yukon-Alaska border or the dam because of all the other ways in which salmon could be killed during their lifecycles.
Built in 1958, Yukon Energy's dam on the Yukon River is a crucial piece of infrastructure, generating enough power to supply on-grid residents with roughly 80 per cent of their electricity during the summer — equivalent to lighting up roughly one million 40 watt light bulbs. The dam has four turbines, a spillway and, at roughly 366 metres, what the company boasts is the "longest wooden fish ladder in the world."
Fish entrained at the Whitehorse dam can be killed in different ways.
"Overall, it was found that the greatest mortality risk to fish was due to strikes/collisions … followed by barotrauma, and shear stress," the study states. Barotrauma refers to injuries brought on by sudden changes in air or water pressure.
The dam has four turbines, with the last one installed in 1985. The study says nearly 12,000 resident fish enter that route alone, and it's one of the more dangerous.
The mortality rate for grayling swimming through the newest turbine is 85 per cent; for Northern pike, it's 99 per cent.
Juvenile salmon were studied separately. The research suggests the larger they are, the higher the likelihood they are killed. For wild, one-year-old chinook, the mortality rate is 58 per cent.
The study states fish are more likely to be sucked into the dam during spring and summer nights. With that, it recommends considering adjusting flows during sensitive migration periods. The study also suggests more research into fish ecology in Schwatka Lake, the dam's reservoir, and taking a hard look at the turbines.
"Fish behaviour can also be influenced to try and guide fish away from potentially harmful passage routes," the study states. "This has been attempted using screens, flow deflectors, lights, electricity, and bubble curtains with some success."
Researchers used discharge data between 2013 and 2024. They also took fish samples, hydroacoustic scans and deployed sensors down intakes at the dam, including the turbines and spillway. Researchers employed similar methods in a 2023 study. This time they were expanded.
'It's just insane how many'
Sebastian Jones, a wildlife analyst with the Yukon Conservation Society, told CBC News the new research not only shows but confirms how perilous the dam can be for fish.
"Some of these turbines are killing almost every freshwater fish that comes through them," he said. "It's just insane how many. That's unacceptable, I think that's a fairly reasonable conclusion."
While mortality rates for juvenile chinook salmon are lower compared to freshwater fish like grayling, Jones said it's no surprise salmon upstream of the dam are "winking out."
"There's no wonder there's no salmon left in the McClintock River that used to support fish camps."
Roughly 88 per cent of the territory's electricity comes from renewable sources, primarily hydroelectricity. The territory has for years been aspiring to significantly reduce greenhouse gas emissions, with ministers saying the Yukon is on firm footing already because of its three dams.
But Jones said dams aren't "green" — they come with significant environmental impacts.
"So when we are contemplating expanding or building new hydro [dams] we need to bear that in mind, you know, are we prepared to wipe out fish runs?" he said. "They're very hard on rivers.
"The research is valuable. It is important, and it will help us design a generating system that reduces the number of fish killed."