A threatened trout species – often used as an indicator of ecosystem health due to its specific habitat needs – has been returned to its native home in a Banff National Park stream for the first time in close to 80 years.
Parks Canada reintroduced at-risk westslope cutthroat trout this summer following rehabilitation over the past decade of a nine-kilometre stretch of Cascade Creek – a controlled and regulated waterbody below Lake Minnewanka reservoir operated by TransAlta.
This marks the start of a three-year reintroduction plan for Cascade Creek, set to be completed by August 2026, with the aim of establishing a self-sustaining population of westslope cutthroat trout in what aquatic experts in Banff are calling a ‘historic conservation milestone.”
“They are the grizzly bear of the water. They are the top of the food chain,” said Mark Taylor, aquatic ecologist team leader for Banff National Park.
“They are consuming bugs, keeping prey populations in check, they are consuming other fish, and without that, it would be like an ocean without sharks or terrestrial landscape without bears.”
In June, Parks Canada transferred about 18,000 westslope cutthroat eggs into specially designed incubation trays placed throughout the creek near Cascade Ponds. These eggs and milt had been collected from adult westslope cut-throat trout from Marvel Lake, where they were fertilized on-site.
Initially incubated in a portable hatchery in Field, B.C., the fry hatched from the trays into their new home in Cascade Creek in July.
“We put the incubation units in a bunch of different locations along Cascade Creek and then the fish would hatch and swim right out into the stream,” said Nicole Sulewski, Cascade Creek field biologist and resource management officer.
“They are now swimming around Cascade Creek, which is super exciting and a long time coming.”
The hatch success rate was more than 97 per cent, much higher than the 80 per cent expected based on experience in other fish reintroduction projects.
Dan Struthers, Cascade Creek restoration project manager, said the number of westslope cutthroat trout being put into the stream considers the creek’s carrying capacity and expected trout survival rates year-over-year.
“Over winter for the first year, we’re expecting 30 to 40 per cent mortality, but the years after that, it’s like five to 10 per cent mortality,” he said.
Once part of the Cascade River, the lower nine-kilometre stretch now known as Cascade Creek was reduced to a mere trickle following construction of the Lake Minnewanka dam in 1941, which dramatically altered the aquatic ecosystem downstream.
After completion of the reservoir, the Cascade River was diverted through the Two Jack Canal system to the TransAlta Cascade hydro power plant.
The newly formed Cascade Creek had dried up halfway towards where it used to connect to the Bow River.
The Cascade River’s historic flows were about 15 per cent of the volume of the Bow River, but construction of the dam reduced the flow by more than 99 per cent.
Because of the dramatic decrease in water flow, fine river sediment began to build up, and as a result, the sediment coated the once rocky stream bed, making it impossible for native fish species like westslope cutthroat trout, which rely on cold, clear water, to spawn in the murky creekbed.
With this unnatural sediment build-up in the riverbed, native fish populations began to struggle because of increasing habitat loss, which was made worse by competition with non-native fish species within the national park like brook trout.
While the 2010 management plan and scientists in the decades preceding that had identified a need to restore aquatic ecosystems, it wasn’t until the the 2013 historic Alberta floods that new life was given to the project.
To prevent a potential dam breach, the spillway at the Lake Minnewanka dam was opened, sending raging waters down Cascade Creek channel, making it all the way to the Bow River for the first time in decades. It followed much of its historic path, including along what was then a grassy ditch alongside the Legacy Trail.
As this powerful torrent ripped through the channel, Struthers said the water swept away the fine sediment that had been clogging Cascade Creek and tore out undersized culverts that had restricted fish movement for decades.
After the floods, Struthers said previous undersized water culverts were replaced with larger ones that fish could pass.
“The flood was a catalyst event for this project,” he said.
Working with project partners like TransAlta and GeoProcess Research Associates, flows into Cascade Creek were increased slightly after the floods and now run at about 0.5 to 0.8 cubic metres per second (m3/s) compared to 0.1 m3/s pre-2013 floods.
The increased flows and other restoration efforts allowed the groundwater aquifer to recharge and reconnect Cascade Creek to the Bow River.
“The channel that we have built is designed for the flows that we are currently getting, so it’s sufficient to maintain our populations,” Sulewski said.
“We will continue to work alongside TransAlta in the management of this stream going forward.”
Over the past decade, extensive measures have been undertaken to ensure the successful reintroduction of westslope cutthroat.
In 2018, Parks Canada worked with a world leader in stream restoration, Robert Newbury, who designed the channel, complete with riffles, pools, and rocky runs to support all stages of life for westslope cutthroat trout.
An excavator was used to restore the channel, with a total of three boulder runs and 14 riffle pool sequences constructed along the creek.
Boulders placed along the channel create deeper pools and a place for westslope cutthroat trout to hide from predators.
Struthers said the pools and riffles provide westslope cutthroat trout with many habitat types to feed, rest and lay eggs.
“Riffle pool sequences are so important because it provides a place for not only cover but also for food and other habitat needs needed to sustain themselves,” he said.
To pave the way for the restoration project, approximately 22,000 non-native brook trout were also removed over several years through electro-fishing – which involves generating a field of electricity in the water that stuns fish so they can be caught.
In addition, a steep waterfall drop has been built downstream closer to the Bow River to prevent non-native fish from coming back into Cascade Creek.
“We solved that problem by building a fish barrier downstream,” Struthers said.
“It’s a one-way fish barrier so fish can leave Cascade Creek and go into the Bow River, but non-native fish can’t come up and jump over that waterfall into Cascade Creek.”
The westslope cutthroat trout reintroduced into Cascade Creek are considered genetically pure.
Many populations throughout the park were assessed, but Marvel Lake was identified as one of the best options because it has a high abundance of very large adult fish – many fish to take eggs from without a risk to the persistence of this population.
While genetically pure, aquatic experts say they are also ancestrally matched to the Bow River basin, which is essential to meet the needs for species recovery.
Sulewski said testing has shown the fish are also disease-free, including from whirling disease.
“We tested our source population, our Marvel Lake population, for a number of different pathogens including whirling disease before we translocated fish here,” she said.
“We have our aquatics invasive species prevention program, which we hope will help keep Cascade Creek free of whirling disease into the future. It’s definitely still a present risk but we hope that we’re mitigating it as best we can.”
Taylor said Parks Canada could not have done this project alone and thanked all partners involved.
“We’ve relied on a lot of outside expertise,” he said.
Aquatic ecosystems are in peril across North America, with native fish populations petering out in many places.
Westslope cutthroat trout have also been reintroduced into other lakes and streams in Banff National Park.
Taylor said saving westslope cutthroat trout is important, noting they are an indicator of ecosystem health and also exist only in this area of Alberta, extending slightly into B.C., Idaho and Montana.
“That’s the only place in the world that westslope cutthroat trout exists,” he said.