Helen and Katherine Lakes

Banff National Park

Parks Canada is working to restore ecological integrity in Banff National Park.

Ecological integrity is intact when:

  • An ecosystem contains the living and non-living pieces expected in its natural region;
  • Processes that make an ecosystem work such as fire, flooding and predation occur with the frequency and intensity expected in its natural region.

Helen Lake and nearby Katherine Lake were historically fishless. In the early 1900s when Parks Canada began stocking mountain park lakes to satisfy the growing number of visitors wanting to fish. Non-native fish, including brook and Yellowstone cutthroat 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.

A Fishless Lake?

Small alpine lakes in the Rockies are often fishless if their outflow streams are too steep for fish to swim up. Stocking fish in these lakes leads to big ecological changes. Fish love eating aquatic insects like mayflies, stoneflies and caddisflies, and with the presence of fish these insects may disappear. Insects perform many functions in a freshwater ecosystem, they:

  • break down organic waste
  • filter particles from the water
  • bring oxygen into bottom sediments

Insects emerging from mountain lakes also provide an important food source for many bird species. Adding fish to a historically fishless lake also creates fish waste that acts as a fertilizer. This can lead to algal growth which adds to the disruption of ecological integrity.

Aquatics staff began treating Helen Lake with rotenone in July 2020, and the following year both Helen and Katherine Lakes received treatment. Using environmental DNA analysis, the team confirmed that both lakes have been restored to their historically fishless conditions, as of 2023. Staff will continue to monitor both lakes to see how insect populations recolonize.

Rotenone, a natural fish toxicant, has been very successful in the removal of fish in high mountain environments like Helen and Katherine Lakes. 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.
A hiker stands on the shore of Katherine Lake 

Stay on this journey with Parks Canada as we protect and restore ecological integrity.
For more information, contact pc.llykaquatics-aquatiquesllyk.pc@pc.gc.ca

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