During the spring and summer, Meghan Rooney sees firsthand how rising water temperatures affect salmon in B.C. waterways.
At 20 C, salmon slow down and seek refuge in cooler areas, said Rooney, science and communications coordinator for Watershed Watch Salmon Society, a charity that works to defend and rebuild the province’s wild salmon population. When temperatures rise above that, fish start to die from the heat, an issue that goes on to have a ripple effect on many different aspects of life in B.C.
“Salmon are incredibly important, not just for our ecosystems,” Rooney said during a Zoom interview from Port Coquitlam. “They feed our forest. They support many different species. They are important culturally for many Indigenous First Nations in B.C.”
Erika Eliason, a fish biologist and associate dean of Kwantlen Polytechnic University’s Faculty of Science, said that fish are ectotherms, meaning their body temperature is the same as their surrounding environment.
“If the water temperature goes from 15 C to 18 C, that means the fish's body goes from 15 C to 18 C,” Eliason said.
“That three-degree change may not seem like much, but it can have a profound impact on the fish's performance and their ability to survive.”
While the ideal water temperature for fish varies by location, when it gets too warm, a fish’s ability to swim, digest a meal, escape a predator and interact with its environment all worsen, Eliason said.
Much of her research shows that fish, including Pacific salmon, experience a higher metabolism in warmer waters, as well as increases in their heart rate, oxygen demand and biochemical reactions. At very high temperatures, their heart begins to fail.
Prolonged heat waves can be “catastrophic” for fish population, Eliason said. For example, when the Fraser River hits 19 to 22 C, Pacific salmon can’t swim upstream, leading many to die on their way to their spawning grounds.
“That's really the biggest trend that we're seeing over and over again,” she said. “Millions of fish can show up to the Fraser River to perform that upper migration … but if the water temperature is too warm, you can get huge numbers of fish that don't make it.”
From 1950 to 2015, summer temperatures in the Fraser River Basin have risen by nearly 1 C, and for many of the basin’s sites, the number of summer days with their water temperature exceeding 20 C has doubled, a University of Northern British Columbia study from 2019 found.
In 2023, the Cheam First Nation in Chilliwack’s Ford Creek experienced a mass die-off of fish due to the heat. Rooney said Watershed Watch assisted the nation by helping to move the fish to a section of the waterway that was cooler and better enriched with oxygen. Ford Creek is just one example of the fish die-offs the charity has helped handle during the summer months in B.C.
Due to the impact of heat waves, the Williams Lake First Nation in the Cariboo region has chosen to not fish its traditional sockeye salmon in the main channel of the Fraser River for the last six years, says Nicholas Coutu, fish and wildlife coordinator at the nation.
“Being at the headwaters, it's their responsibility — and mine now also — to steward those fish and allow them to get to their nursery, so that other people all the way down the Fraser, into the ocean, can have future fish,” he said.
“If they continue doing their traditional harvesting, it will prevent those fish from spawning. So they have the weight of all that responsibility on them.”
What's being done
Droughts make ledges for fishing inaccessible to Willams Lake First Nation
Over the last two years, as water levels have lowered, the ledges along the Fraser River on Williams Lake First Nation territory have been too high above the water for fishing.
These ledges are along steep cliff canyons, which the Secwépemc people, including the Williams Lake Nation, traditionally use wide nets to collect dozens of fish, said Nicholas Coutu, the nation’s fish and wildlife coordinator.
“It’s a glaringly obvious impact of climate change and low water because of drought,” he said.
The water levels are the lowest they have been in over 6,500 years, which is how long the nation has been fishing along the cliffs, Coutu said.
The most traditionally sought after fish by the nation is sockeye salmon, which is in steep decline. During the mid-1990s, about 800,000 sockeye salmon returned to its nursery to spawn. In 2024, the Pacific Salmon Foundation forecast a total of just 560,000 sockeye in the Fraser for that year.
At the Chilcotin River, a massive landslide in July 2024 prevented the nation from accessing its other fishing site, so Coutu drove up north of Smithers and received one-thousand sockeye from the Gitxsan First Nation.
“It was sad in a way, but it was very fulfilling to see all the First Nations people coming together for the thing they love and cherishing that gift from another First Nation because they didn't have any,” Coutu said.
Tŝilhqot'in National Government was contacted for comment for this story.
This story was written by a student in Kwantlen Polytechnic University's Journalism program as part of a partnership between KPU and simplymastery.
