Margaret Lake

Banff National Park

Parks Canada is restoring critical habitat for westslope cutthroat trout in Banff National Park. These fish once lived in abundance in the cold, fresh waters of Margaret Lake. Now, the Alberta population is listed as threatened under the Species at Risk Act.

In the early 1900s Parks Canada began stocking mountain park lakes to satisfy the growing number of visitors wanting to fish. Non-native fish, including brook and rainbow trout, were introduced and flourished, displacing native species. Parks Canada no longer stocks lakes with non-native fish, but these past stocking practices continue to impact the park’s aquatic ecosystems. The westslope cutthroat trout has declined to 10% of its historic range.

Westslope cutthroat trout are a species at risk for several reasons:
  • Displacement by non-native fish
  • Competition with brook trout for resources
  • Hybridization with rainbow and Yellowstone cutthroat trout
  • Loss and damage to stream habitat
  • Increasing water temperature and other factors related to climate change

Parks Canada‘s four step process to save threatened trout: 

1. Identify secure habitat

Aquatics staff determined that if Margaret Lake had a year-round fish barrier, it would be a suitable and secure habitat for threatened westslope cutthroat trout. Margaret Lake’s outflow stream has a stepped cascade that fish can swim up in high water. Aquatics staff will enhance the existing cascade using controlled detonations in the fall of 2022. The resulting 2.5-3 metre waterfall or barrier will prevent non-native species or hybrid cutthroat trout in Hector Lake from returning to Margaret Lake.

2. Remove non-native fish

Non-native brook trout and hybrid cutthroat trout will be removed from Margaret Lake using a fish toxicant, rotenone, in summer 2022 and a follow-up application will be required in summer 2023. Each application will take one day and Parks Canada staff will stay on site to ensure rotenone levels safely decrease. They will apply a neutralizing agent to work alongside rushing water and sunlight to help breakdown the rotenone. 

Rotenone, a natural fish toxicant, has been very successful in the removal of fish in high mountain environments like Margaret Lake. It is derived from the roots of plants in the bean family and has been used around the world when working with fish, including national parks in eastern Canada. It is not dangerous to people, mammals or birds unless ingested in unreasonably large quantities. 
3. Reintroduce westslope cutthroat trout

Once monitoring ensures that the removal of all non-native fish in Margaret Lake has been successful and aquatic invertebrate communities have been re-established, the re-introduction of native westslope cutthroat trout will begin. 

4. Monitor success

Once westslope cutthroat trout are re-introduced the team will monitor Margaret Lake until it supports a healthy and self-sustaining population of westslope cutthroat trout.

Stay on this journey with Parks Canada as we protect and restore habitat for species at risk.
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