Park Canada is working to restore critical habitat for westslope cutthroat trout in Banff National Park. In the past, westslope cutthroat trout could be found in abundance in the cold, fresh waters of Hidden Lake. Now listed as threatened under the Species at Risk Act, Parks Canada is taking steps to restore safe refuges for westslope cutthroat trout and rebuild their population in Banff National Park.

In the early 1900’s Parks Canada began stocking its mountain lakes to satisfy visitors who wanted to fish. A number of non-native species, including brook and rainbow trout, were introduced and flourished in their new homes. Parks Canada does not stock its lakes with non-native fish anymore but past stocking practices have impacted park aquatic ecosystems.

Westslope cutthroat trout are a species at risk because of:
  • Displacement by non native fish
  • Competition with brook trout for resources
  • Hybridization with rainbow and yellowstone trout
  • Loss and damage to stream habitat
  • Increasing water temperature due to climate change
Parks Canada is committed to a four step process to save threatened trout:

Identify secure habitat
Remove non-native fish
Reintroduce westslope cutthroat trout
Monitor success

To restore critical habitat, non-native brook trout need to be removed from Hidden Lake. Since 2011, Parks Canada aquatic staff have tried to rid Hidden Lake of non-native brook trout through angling, gill netting and electro fishing. None of these manual removal techniques have been effective at this site.

Rotenone, a natural fish toxicant, has been very successful in the removal of fish in high mountain environments much like Hidden Lake. It is derived from roots of plants in the bean family and has been used in fish practices around the world and in national parks in eastern Canada. It is not dangerous to people, mammals or birds unless ingested in extremely large quantities.

With the help of partners, our aquatics team completed two treatments of Hidden Lake with rotenone in 2018 and 2019. Each treatment took one day and Parks Canada staff stayed on site to ensure rotenone levels safely decreased through natural breakdown. In 2020, Hidden Lake was monitored to verify the efficacy of the rotenone treatments. Once removal all of non native fish in Hidden Lake is confirmed, re-introduction of native westslope cutthroat trout will begin.


Why all the fuss about fish?

Protecting species at risk and aquatic restoration are priorities for Parks Canada.

  • Westslope cutthroat trout are a fussy fish or what we call an indicator species. They thrive in cold, clean and unpolluted waters. A healthy population helps to indicate a healthy ecosystem.
  • Healthy aquatic ecosystems are integral to the health of the whole ecosystem.


Stay on this journey with Parks Canada as we protect and restore habitat for species at risk.
For more information, contact