Eurasian Water-Milfoil

Description

Eurasian water-milfoil (Myriophyllum spicatum) is an invasive aquatic plant native to Eurasia and North Africa that was first recorded in Canada in Lake Erie in 1961. It grows below the water’s surface and can form dense mats that crowd out native aquatic plants, alter fish and wildlife habitat, and interfere with swimming, boating, and other recreational activities. Eurasian water-milfoil spreads easily from small plant fragments, which can be transported between waterbodies on boats, trailers, fishing gear, and other aquatic equipment.

  • Scientific name: Myriophyllum spicatum 

  • French name: myriophylle à épis 

  • Common name(s): Eurasian spiked water-milfoil 

  • Distribution: Found in Quebec, New Brunswick, Prince Edward Island, Manitoba and British Columbia.

  • Regulatory Status: Eurasian water-milfoil is not a federally regulated invasive plant in Canada. However, it is regulated as a Prohibited Noxious Weed in Alberta, a Management Species by the British Columbia Provincial Priority Invasive Species List, and a Restricted species under the Ontario Invasive Species Act.  

Image of Eurasian Water-Milfoil

© abcdefgewing via iNaturalist.org, used under CC-BY-NC

Introduction and Spread

Eurasian water-milfoil, also known as the “zombie plant”, likely arrived in North America through the aquarium trade, or in ballast water from shipping in the 1940s. The first record in Canada was from Lake Erie in 1961 (Aiken et al. 1979). Since then, it has become one of the most widespread and problematic aquatic invasive species in North America due to its competitive growth habits and ability to spread vegetatively by rhizome fragments (MNR 2021). These fragments can break easily, allowing Eurasian water-milfoil to be transported long distances by boats, boat trailers, fishing gear, and other aquatic equipment (NYIS 2025; Smith and Barko 1990). It can also spread naturally by water currents, wind and waterfowl, as well as seasonal autofragmentation (Aiken et al. 1979). It is able to rapidly colonize areas that have experienced some form of disturbance, which can further promote fragmentation and spread.

Eurasian water-milfoil is native to Eurasia and North Africa. Outside of its native range, it has spread across every continent except Antarctica (MNR 2021). In North America, it is present throughout most of the United States, all of the the Great Lakes as well as in-land lakes in southern and eastern Ontario (MNR 2021; EDDMaPs 2025). It can be found in six Canadian provinces including Quebec, New Brunswick, Prince Edward Island, Manitoba and British Columbia (NCC 2025, iNaturalist 2025). It is a provincially regulated species in Alberta, British Columbia, and Ontario. 

Habitat

Eurasian water-milfoil is most commonly found in slow or stagnant waters, such as ponds, marshes, lakes with little disturbance, or along sheltered portions of streams (i.e., coves, inlets). It is able to rapidly colonize areas that have experienced some form of disturbance. It is most common in depths of 1 – 3 m but can grow up to depths of up to 10 m; growth is limited in very shallow waters due to fluctuating temperature and water levels. The plant’s rooting depth and growth form vary with water depth and clarity—shallow, turbid waters promote horizontal, matted growth near the surface, while in deeper, clearer waters, it forms long strands that do not reach the surface or form dense canopy stands. Well-adapted to a range of conditions, Eurasian water-milfoil thrives in both nutrient-rich and nutrient-poor environments, tolerates a broad pH range (5.4–11), and grows best in alkaline waters and temperatures between 15–35°C (Smith and Barko 1990).

Identification

  • Height and Stems: Submerged; Stem is a leafy shoot, can be long and spaghetti-like (0.5 – 7 m long), branching at water surface, forming dense canopies. Tip of the stem usually reddish and thin, getting thicker below the flowers. 

  • Leaves: Whorls (circles) of feather-like, green leaves are centered around nodes along the stem, with 3 – 6 (typically 4) leaves per node. Each leaf has 12 – 24 filiform or threadlike divisions. 

  • Flowers: Emergent, grow on terminal spikes above the water. Arranged in whorls (circles) around spike, pink-red hue. Flowers from late July to early August; upper flowers are male, the lower flowers are female. 

  • Fruit: Red, berry-like.  

  • Roots: Can be rooted or unrooted to sediment. No overwintering structures (turions). Small buds may be present and develop from a single root, initially at the base. 

Image of eurasian water-millfoil leaves

Eurasian water-milfoil leaves

Image of eurasian water-milfoil fruit

Eurasian water-milfoil fruit

Closeup image of eurasian water-milfoil

Eurasian water-milfoil stem

  • Lookalikes: Canada has a native species of water-milfoil, the northern water-milfoil (Myriophyllum sibiricum), that could be mistaken for the invasive plant.

Impacts

  • Eurasian water-milfoil forms dense floating mats of vegetation that can outcompete native aquatic plants and alter a lake’s natural ecosystem. Dense mats block available light and impact water clarity, and its extensive root system reduces space and access to nutrients in the sediment for other plant species (Aiken et al., 1979). As a result, significant declines in native submergent plant species richness and abundance have been observed in infested lakes (Madsen et al., 1991).  

  • Dense mats also reduce macroinvertebrate abundance and negatively impact fish populations, by altering water quality, reducing suitable sites for spawning, and reducing dissolved oxygen levels (NYIS 2025). A reduction in dissolved oxygen levels caused by the decomposition of plant matter can kill fish and contribute to algal blooms (MNR 2021).  

  • Eurasian water-milfoil mats reduce spawning success for salmonids by covering open gravel areas which are ideal sites for spawning. Dense mats can also lead to an overpopulation of forage fish like bluegill, while predatory fish like largemouth bass decrease in numbers, as they have more difficulty accessing fish prey hidden in the vegetation (Menninger 2011). 

  • Thick mats are considered unsightly and decrease the aesthetic value of beachfront properties, creating stagnant conditions ideal for mosquitos. Several studies in the USA have demonstrated that Eurasian water–milfoil can significantly reduce lakefront property values (Olden and Tamayo, 2014).  

  • Excessive growth can also clog industrial and power generation water intakes and restrict the operation of flow metering devices in flood control channels (Aiken et al. 1979). 

Life cycle

Eurasian water-milfoil can spread sexually by seed as well as vegetatively through stem fragmentation and stolon growth. In the Great Lakes region, Eurasian water-milfoil begins to break dormancy in early spring before other native macrophytes and initiates growth as water temperatures approach 15°C (Smith and Barko 1990). Flowering spikes emerge above the water line once the plant has reached the surface, typically June to July. Fruits develop later in July or August and continue until September. The plant reaches its peak growth and biomass shortly after flowering, when milfoil stems begin to branch and form dense clusters, blocking available sunlight to other submerged plants. Soon after this peak biomass in late summer to early fall the plant begins a natural process called autofragmentation, whereby small branches begin to develop roots, break away from the parent plant, and float until they lose buoyancy, at which point they sink and root in the sediment, ultimately forming new plants. Towards the end of the growing season, some plants die back to their root crowns, while others overwinter intact in an evergreen form. Reserves are stored in overwintering roots and shoots (Aiken et al., 1979).

What You Can Do

You can help prevent the spread of Eurasian water-milfoil by:

  • Clean Drain Dry: Inspect your boat, trailer, paddles, fishing gear, and boots for mud, plant parts, or small critters. Remove and dispose of anything you find before leaving the water.

  • Don’t Let it Loose: Never dump your pets or plants into lakes or streams. Dumping aquariums and aquarium plants into waterbodies can spread invasive aquatic plants like Eurasian water-milfoil.

  • Educate: Learn to identify Eurasian water-milfoil and spread awareness about the ecological risks posed by Eurasian water-milfoil and encourage responsible practices in your community. 

  • Reporting: Report eurasian water–milfoil and any invasive species to the appropriate provincial authorities such as provincial invasive species councils or report using free tools such as EDDMapS and iNaturalist.

Other Resources

  1. Aiken, S. G., Newroth, P. R., and Wile, I. 1979. The biology of Canadian Weeds.: 34. Myriophyllum spicatum L. Canadian Journal of Plant Science, 59(1), 201-215. 
  2. Borrowman KR, Sager EP, and Thum RA. 2014. Distribution of biotypes and hybrids of Myriophyllum spicatum and associated Euhrychiopsis lecontei in lakes of Central Ontario, Canada. Lake and Reservoir Management. 30: 94-104.  
  3. Cooper AL, DeBues MJ, and Sager EP. 2017. Eurasian watermilfoil management on Big Cedar Lake, Ontario: Progress Report. Pp 1-19. 
  4. EDDMapS. 2025. Eurasian watermilfoil (Myriophyllum spicatum L.). [Accessed 2025 June 18] https://www.eddmaps.org/project/midwest/distribution/viewmap.cfm?sub=3055. 
  5. Extension Lakes, EWM Hand Removal. 2013. https://www.youtube.com/watch?v=CfsEDyAwQP4  [Accessed 2025 June 21]. 
  6. FLCA. Farlain Lake Community Association. 2025. Eurasian watermilfoil – dealing with the threat. https://farlainlake.ca/our-lake/eurasian-watermilfoil [Accessed 2025 June 21]. 
  7. iNaturalist. Eurasian Water-Milfoil. 2025. [Accessed 2025 June 18]  https://www.inaturalist.org/observations?taxon_id=78157. 
  8. Madsen J., Sutherland J., Bloomfield J., Eichler L., Boylen C. 1991. The decline of native vegetation under dense eurasian watermilfoil canopies. Journal of Aquatic Plant Management. 29: 94-99. 
  9. Menninger, H. 2011. Review of the science and management of Eurasian watermilfoil: recommendations for future action in New York state. New York Invasive Species Research Institute. http://fingerlakesinvasives.org/ wp-content/uploads/2014/03/NYISRI-EWM-Report_Final_11Nov2011.pdf, accessed 5 February 2020.  
  10. MNR. Ministry of Natural Resources. 2021. Eurasian water milfoil. [Accessed 2025 June 10] https://www.ontario.ca/page/eurasian-water-milfoil.  
  11. NCC. Nature Conservancy of Canada. 2025. Eurasian milfoil. [Accessed 2025 June 10] https://www.natureconservancy.ca/en/what-we-do/resource-centre/invasive-species/eurasian-milfoil.html. 
  12. Newman, R.M. 2004. Invited review: biological control of Eurasian watermilfoil by aquatic insects: basic insights from an applied problem. Archive for Hydrobiology 159:145-184. 
  13. NYIS. 2025. New York Invasive Species (IS) Information. Eurasian watermilfoil. [Accessed 2025 June 15] https://nyis.info/species/eurasian-watermilfoil/. 
  14. Olden, J.D. and M. Tamayo. 2014. Incentivizing the public to support invasive species management: Eurasian milfoil reduces lakefront property values. 9: e110458.  
  15. Sesin, V., Dalton, R.I., Boutin, C., Robinson, S.A., Bartlett, A.J. and F.R. Pick. 2018. Macrophytes are highly sensitive to the herbicide diquat dibromide in test systems of varying complexity. Ecotoxicology and Environmental Safety 164: 325-333. 
  16. Smith, C.S. and Barko, J.W. 1990. Ecology of Eurasian watermilfoil. Journal of Aquatic Plant Management. 28(2): 55-64. 

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