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Water Quality

Eurasian Watermilfoil in British Columbia

This brochure has been produced to answer the more frequent enquiries received by the Ministry of Environment on Eurasian watermilfoil and to provide you with general information on related water management concerns.

What is the Problem?

Aquatic plants are an important part of the biology of our lakes and other water bodies. They provide food, habitat and rearing areas for a wide variety of organisms. Vegetation helps to stabilize lake bottoms and aerate the water. However, some aquatic plants, such as Eurasian watermilfoil, also can have undesirable effects, especially when they are too abundant or become established in unwanted locations.

Eurasian milfoil cover

In British Columbia, problems caused by Eurasian watermilfoil include:

  • growing and spreading rapidly
  • invading and replacing native plant communities
  • obstructing swimming, boating, waterskiing and fishing
  • reducing the appeal of beach areas due to the accumulation of plant debris
  • impeding flood control, water conservation, drainage and irrigation works
  • reducing the economic benefits of tourism where dense growth limits recreation

millfoil leaf

Eurasian watermilfoil is not native to North America. It was first observed in British Columbia in 1970 in Okanagan Lake. The plant has spread since to Shuswap and Mara Lakes, to Christina and Champion Lakes in the Kootenays, to all the main lakes in the Okanagan Valley and to numerous water bodies in the Lower Mainland. Also, isolated populations were discovered on Vancouver Island in 1985, and in Nicola Lake in 1991.

Many uninfested water bodies in these areas and elsewhere in British Columbia remain susceptible to the introduction of this plant.

How Does it Grow and Spread?

Eurasian watermilfoil is a perennial, which grows from a fibrous root system on a variety of bottom types. During the spring and summer months, when growth is rapid, plants may reach the water surface from depths exceeding five metres.

Floating plant fragments produced by waves and boaters are spread by water currents, making the plant difficult to contain. New plants develop when the fragments sink, rooting best in protected locations.

Boats and boat trailers carrying plant fragments are thought to be the most common form of spread from one water body to another.


Management strategies currently in use in British Columbia include:

  • preventive efforts (e.g. surveillance of non-infested areas and public information to discourage spread, particularly by boaters)
  • placing bottom coverings on new populations to prevent lake-wide infestations
  • root removal (maintenance of priority areas by rototilling or shallow water cultivation)
  • harvesting (cosmetic control by cutting the plant below the water surface)

What Can You Do?

  • Reduce spread of watermilfoil and other aquatic weeds by clearing all plant material from boats, motors, trailers, wet wells and anchors. Dispose of plants far away from water bodies.
  • Learn how to identify Eurasian watermilfoil.
  • Report suspected new infestations to any Ministry of Environment.
  • Contact local authorities and seek expert advice when concerned about aquatic plant problems in your community.

Originally published in June 1993

updated: July 2011


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