Advocates call on Yukon Energy to consider salmon in plans to relicense Mayo dam
Julien Greene | CBC News | Posted: February 5, 2025 7:56 PM | Last Updated: February 5
One biologist says vast habitat above facility will remain off limits to chinook
Plans to make the hydroelectric dam north of Mayo fish-friendly don't include measures to help chinook salmon, a fisheries biologist says.
Lars Jessup, who often works with the First Nation of Na-Cho Nyӓk Dun, said now is a crucial time to ensure critical spawning and rearing habitat above the dam doesn't continue to be blocked off for longer than it already has.
"Their preferred spawning habitat — the beautiful lakeheaded spawning habitat that's upriver — has been unavailable to them, and so this stock has been throttled," Jessup said at a recent Yukon River Panel meeting in Anchorage, Alaska.
"Na-Cho Nyӓk Dun very much needs allies to overcome the challenges that exist in this system."
Yukon Energy is currently working to relicense the facility for five years. The Yukon Environmental and Socio-Economic Assessment Board recently launched a public comment period. Residents can have their say on the project until Feb. 17.
Built in the 1950s, the dam has since then obstructed the upriver migration of fish, including chinook, whose numbers are a fraction of what they once were. Yukon Energy states in a report there are no salmon upstream of the dam anymore.
Above the facility is Mayo Lake, whose headwaters include vast wetland complexes. Some, like the Roop, have been relatively insulated from rising lake levels caused by the dam.
These areas, Jessup said, should be unlocked.
"Past surveys on the upper Mayo River have concluded that significant chinook spawning and rearing habitat still exists upstream of the dam," he said. "We feel there is a significant opportunity here to restore what was once a really vibrant ecosystem.
"This upper Mayo River is an area that once was likely rich with marine derived nutrients and has not had that opportunity for about 70 years."
Jessup said freshwater fish like inconnu, Arctic grayling and whitefish would also benefit from upriver access.
A spokesperson with Yukon Energy said in an email to CBC News a small fraction of Yukon River salmon reach the Mayo River system — on average, as low as 0.2 per cent.
"Yukon Energy recognizes the lasting impacts of the Mayo Hydro Facility, and we are working collaboratively with partners to identify mitigations," Keely Bass said.
What do Yukon Energy's fish passage plans look like?
Unlike the hydroelectric dam in Whitehorse — which Yukon Energy is also in the middle of relicensing — the one in Mayo has never had an upriver fish passage, despite Na-Cho Nyӓk Dun having long advocated for one.
Part of Yukon Energy's proposal includes replacing the control structure dam, which allows for water storage in Mayo Lake so that electricity can be generated during the wintertime. As part of the process, the Crown corporation would also install a fishway that would allow fish swimming upriver to pass through the dam.
Elizabeth MacDonald, a member of the Yukon River Panel, said the fishway that is being proposed is only for freshwater fish like grayling.
"Currently, they are not going to design it to accommodate chinook," she said. "If we can get that habitat opened up again it'll be more productive than where those fish are spawning right now, and chinook are very smart and they know where to find a good place to put their eggs."
Bass, with Yukon Energy, clarified that a design for the new control structure dam would allow for the species to pass through both up and downstream.
The facility consists of two dams that yoke the Mayo River. About 35 kilometres downriver is the larger of the two: the Wareham dam, which is 32 metres tall. Technically, the structure can allow fish to pass downriver because it has a spillway, a large concrete chute that's in poor condition. But fish that swim through there can be hurt or killed.
The spillway sustained damage from high water levels in 2020. Yukon Energy said through a separate process it will consider permanent repairs to make the spillway safer for fish.
Yukon Energy hasn't proposed any plans for upstream fish passage at the Wareham dam.
Bass said Yukon Energy has started to discuss fish passage options at the dam with Na-Cho Nyӓk Dun and the territorial government, noting construction costs would require "significant funding support."
Jessup, the biologist, said a fishway at the Wareham dam would need to be more than 360 metres long, about equivalent to the one at the Whitehorse dam.
"Fish passage solutions at the Wareham dam are sure to be very economically costly," Jessup said. "That will require funding sources outside of the Yukon Energy Corporation."
If Yukon Energy took on the fishway project itself, costs would inevitably hit ratepayers, he said.
Clarifications:- This story has been updated to reflect the fact that, if built, the new control structure dam proposed by Yukon Energy would be able to accommodate chinook salmon swimming upstream into Mayo Lake. February 5, 2025 11:39 PM