Eurasian Watermilfoil

Eurasian watermilfoil (Myriophyllum spicatum) is a perennial aquatic invasive plant that established in the early 1970s in the Okanagan and has spread to select waterbodies in the Thompson/Okanagan, Central Kootenay, East Kootenay, Lower Mainland, and coastal regions. Many un-infested waterbodies in these areas and elsewhere in BC remain susceptible to its spread.

Eurasian watermilfoil inhibits the flow to waterways, irrigation ditches, and drainage canals, where it has the potential to increase maintenance costs. Plants form thick, underwater stands of tangled stems and vast mats of vegetation on the water's surface, especially in shallow, nutrient-rich water. These mats can limit recreation, such as boating, swimming, and fishing. They can also detract from the aesthetic appeal of the shoreline, resulting in decreased desirability of nearby residential areas. Dense stands also result in stagnant waters which increase breeding grounds for mosquitoes.

This invasive plant has the ability to outcompete with and replace native plant communities, reducing overall biological diversity and reducing water quality. 

Listed under the Community Charter Act, Eurasian watermilfoil is identified by reddish flowering spikes that emerge 5-10 cm above the water, with small yellow flowers that have 4 petals. Flowers are alternate and attached directly to the stem. Plants typically grow between 1-4 m but can extend up to 10 m. Bright green feathery leaves grow 3 cm long, in whorls of 3 or 4, and each leaflet has 11-16 pairs.

Eurasian watermilfoil is usually found in still or slow moving water, and reproduces by underground stems (rhizomes), seeds, buds and stem fragments. Floating plant fragments are most commonly dispersed from one water body to another by water currents, animals and boats/trailers. To prevent its spread:

  • Minimize disturbance near infested areas; and
  • Remove any plant material from boats, anchors, trailers, fishing gear and other equipment before leaving the water body. Please dispose of plants far from water bodies to prevent a new infestation. 

Although plants can be removed either by hand or by mechanical means, it is not recommended unless all plant fragments can be removed. For more information on integrated management practices that offer suggestions for mechanical, biological and chemical control options, please view our Eurasian watermilfoil factsheet.