General: Eurasian Watermilfoil is a submerged, rooted, aquatic perennial.
Flowers: Are small and yellow, with 4 petals, growing on reddish spikes that rise above the water and are 5 – 15 cm long. Flowers are usually arranged in whorls.
Stem: Mostly grow underwater and branch near the surface.
Leaves: Bright green, feathery leaves are arranged in whorls of 3 – 5 off the stem; each whorl has 12 – 21 thread-like leaflets.
Fruit: Segmented capsules containing 4 nearly round seeds.
Habitat and Origin
Eurasian Watermilfoil is native to Europe, Asia, and Africa. It was introduced to North America either through the aquarium trade or in ships’ ballast water.
It is often found in still or slow-moving water bodies, such as lake shorelines, sloughs, irrigation canals, marshes, and streams. Water bodies that have experienced disturbances like nutrient loading, intense plant management, or abundant motorboat use are especially susceptible. Eurasian Watermilfoil can also tolerate the brackish water of tidal creeks and bays.
Propagation & Vectors of Spread
Eurasian Watermilfoil primarily reproduces vegetatively through rhizome and stem fragmentation. Fragments of plants can grow into entirely new individuals. It can also reproduce by seed; however, germination rates are poor.
Eurasian Watermilfoil is most commonly spread from one water body to another by water currents and animals as well as boats or trailers and fishing gear. Boat propellers can break off plant fragments and spread them to new areas. The seeds can also spread in the wind.
Ecological, Economic, & Health Impacts
- Tolerates cold water temperatures, allowing Eurasian Watermilfoil to photosynthesize before native species, reducing light penetration early in the season.
- Shades out native species.
- Creates stagnant waters, increasing mosquito breeding areas.
- Decreases oxygen levels in the water due to the decay of the large mats of Eurasian Watermilfoil in the fall.
- Decreases available habitat for large predatory fish.
- Clogs waterways, irrigation ditches, and drainage canals, adding to maintenance costs.
- Decreases aesthetic appeal of the shoreline, decreasing desirability and value of adjacent residential areas.
- The decreased aesthetic value of lakefront properties also negatively impacts tourism.
What Can I Do?
Eurasian Watermilfoil is NOT currently found throughout the Sea to Sky Corridor, so the best approach to controlling its spread is by PREVENTION.
Learn to identify Eurasian Watermilfoil: Use the images presented in this profile page to learn how to identify Eurasian Watermilfoil.
What to do if you spot it: You can report any Eurasian Watermilfoil sighting by clicking here.
- Clean, Drain, Dry all watercraft. Rinse all mud, debris, and plant fragments from all equipment, wading gear, and boats.
- Ensure all plant parts are bagged and covered during transport to the designated disposal site (e.g. landfill).
- Do not plant Eurasian Watermilfoil in an aquarium or water garden.
- Do not dispose of aquarium plants in water bodies.
- Do not compost!
- Removal by hand (by raking and seining) or with machines is possible but not recommended due to the risk of spreading stem fragments.
- Bottom barriers, which consist of sheets of material like fiberglass, polypropylene, or PVC that are anchored to the lake bottom, are most appropriate to control growth in localized areas. They prevent plant growth by blocking sunlight.
- The BC Government has also developed a barge-mounted device called a rotovator, which tills the roots from the sediment. Floating roots then have to be removed from the water.
Herbicides cannot be applied in aquatic environments in Canada. Herbicide control is not recommended for this species.
- Some biological agents exist, including a weevil (Eurychiopsis lecontei) whose larvae bore down through the stems, introducing diseases that suppress growth and a midge (Cricotopus myriophylli) whose large feeds on the plant stems, reducing overall plant integrity and suppressing plant growth.
- However, no single species is known to make enough impact to be helpful as a biocontrol agent.
- In waterbodies where it is possible to manipulate the water levels, dehydrating the root crown for several weeks has been successful in reducing the biomass of the infestation.
- Water manipulation in the winter can also be used to freeze the plant to death.
- Alberta Invasive Species Council, Eurasian Watermilfoil Factsheet, https://secureservercdn.net/22.214.171.124/yjc.cc8.myftpupload.com/wp-content/uploads/2020/07/FDIP_FS-EurasianWatermilfoil.pdf?time=1657792559
- Central Kootenay Invasive Species Society, Eurasian Water Milfoil, https://ckiss.ca/species/eurasian-water-milfoil/
- Global Invasive Species Database, Myriophyllum spicatum, http://www.iucngisd.org/gisd/species.php?sc=278
- Gull Chain of Lakes Association, Eurasian watermilfoil, https://www.gcola.org/eurasian-watermilfoil#:~:text=Minnesota%20Sea%20Grant%20%28U%20of%20M%29%20Eurasian%20watermilfoil,often%20confused%2C%20usually%20has%205%20to%209%20pairs
- Invasive Species Compendium, Myriophyllum spicatum (spiked watermilfoil), https://www.cabi.org/isc/datasheet/34941
- Invasive Species Council of BC, Eurasian Watermilfoil, https://bcinvasives.ca/invasives/eurasian-watermilfoil/
- Lake George Association, Eurasian Watermilfoil, https://www.lakegeorgeassociation.org/educate/science/lake-george-invasive-species/eurasian-milfoil/
- New York Invasive Species Information, Eurasian Watermilfoil, http://nyis.info/invasive_species/eurasian-watermilfoil/
- Ontario’s Invading Species Awareness Program, Eurasian Water-Milfoil, http://www.invadingspecies.com/eurasian-water-milfoil/