An expert on British Columbia鈥檚 salmon populations says the massive landslide that blocked off part of Canada鈥檚 largest sockeye salmon run has created an unprecedented situation potentially putting the already struggling fish at even more risk.

Scott Hinch, the associate dean at the University of British Columbia鈥檚 Pacific Salmon Ecology and Conservation Laboratory, said the debris piled 30 metres high and 600 metres long blocking the Chilcotin River could cause problems for chinook and sockeye populations both while the water is being held back, and when it eventually bursts free.

鈥淭hese are natural events, but what鈥檚 unusual about this event is it鈥檚 occurring at a time when the rivers are way warmer than they used to be,鈥� he said in an interview Thursday.

鈥淎nd that creates this unprecedented lack of understanding of what鈥檚 going to happen to these fish.鈥�

The sockeye are on their way to Chilko Lake, where they will spawn. But to get there, they have to get through Farwell Canyon, close to where the dam of rock and mud is in the way.

鈥淭hey would be starting to trickle through naturally now and then in about a week and a half, 10 days or so, the peak of that run will be into the Chilcotin,鈥� he said.

鈥淭hey鈥檙e coming up the Fraser right now, these fish.鈥�

The Chilcotin is a tributary of the Fraser River and officials with the province and Cariboo Regional District say it鈥檚 uncertain if the lake building behind the dam will burst or if it will top over the debris. The B.C. government said a release could swell the Fraser River for hundreds of kilometres, potentially setting off dozens of emergency evacuations and alerts.

Hinch said the warmer Fraser River is already nearly lethal for the salmon, and if the fish get held back from entering cooler glacier-fed waters, that could be dangerous.

鈥淪o, what鈥檚 happening right now is, with the reduced water flow downstream, that water is going to be warmer as a start. It鈥檚 also going to possibly be less accessible. So, these fish are going to be holding in warmer water and low flows, either in the Chilcotin system or in the Fraser system, he said.

Williams Lake First Nation Chief Willie Sellars said the situation with the salmon run is 鈥渋ncredibly concerning.鈥�

He said the First Nation is worried about what will happen to the fish after the large lake pooling behind the landslide breaks loose.

鈥淲hat is that going to do to every single one of those sockeye and chinook that are swimming up the Fraser River looking to spawn in those other tributaries?鈥� he said.

Hinch said one of the problems is that there鈥檚 no way to know how the debris sent flowing down the rivers will eventually settle.

鈥淚f not full barriers, it could create partial barriers, it could create areas where it鈥檚 more difficult for the fish to get around,鈥� Hinch said.

鈥淜eep in mind that these fish have all stopped feeding about a month ago. And so, they鈥檙e migrating up on reserves.鈥�

There鈥檚 also a risk that new rock and debris in the water could affect the salmon鈥檚 ability to navigate using their sense of smell, a skill imprinted on them as fry.

鈥淭hey are imprinted on unique chemicals that are in their home watershed. That chemical composition is disrupted by landslides, because you now have other organic chemicals coming into the river, at high concentrations, that aren鈥檛 part of their home stream smell,鈥� he said.

Sellars said this year was already anticipated to be a low run year.

鈥淢aybe it鈥檚 better that something like this happened on the low year, but then it鈥檚 also pretty devastating to that run that鈥檚 going to be heading up the Chilcotin and four years from now, there is going to be no fish,鈥� he said.

At a news conference Thursday, Nathan Cullen, the minister of water, land and resource stewardship, said the government knows that the water is critical spawning habitat for salmon and other fish and that the sockeye are on their way.

He said the government was 鈥渋nitiating early plans as to what we can do to make sure that those stocks remain intact.鈥�

Hinch said there鈥檚 not much that can be done prior to the dam breaking.

鈥淎ll we can do is hope that the temperatures that these fish are holding in isn鈥檛 doing irreparable damage to them for too long of a period of time. And that the fish get into the Chilcotin once the river is amenable for migration.鈥�

In 2019, a landslide partially blocked the Fraser River and created an impassable barrier to key salmon populations that spawn in the Upper Fraser watershed.

Rescue efforts to get the trapped salmon beyond that slide included shooting them through a so-called salmon cannon, capturing the salmon, then transporting them on a truck or helicopter past the site and finally creating a permanent fishway to help them get past the slide.

Ashley Joannou, The Canadian Press