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Eurasian Water Milfoil

(Myriophyllum spicatum)

Common Names

Spike watermilfoil, milfoil, EWM


Eurasain watermilfoil or EWM is a new invader to Montana, that continues to expand its territory.  Eurasian watermilfoil is an incredibly invasive submersed aquatic plant. Like the native milfoils, the Eurasian variety has slender stems whorled by submersed feathery leaves and when the plant reaches the water’s surface, it curls to lie parallel with the surface. Leaves are 2-4 cm long, feather-like, and arranged in whorls of 4 around the stem. The leaves are thread-like and uniform in diameter. They typically have greater than 14 leaflet pairs per leaf. This plant will only flower if it reaches the surface.  Small red to pinkish four-petal flowers appear on a flower spike that is 4-8 cm long held erect above the water surface.   Without flowers, EWM is nearly impossible to distinguish from other milfoils and in order to correctly identify this plant, DNA testing must be done.


Eurasian watermilfoil grows in a diverse range of aquatic habitats, including rivers, reservoirs, canals, lakes, slow-moving streams, and fish ponds. It is usually found in waters less than 15 feet deep.

Currently found in the following counties:

Broadwater, Flathead, Gallatin, Jefferson, Lake, Sanders, Valley


Interesting Facts

In the past, this plant has been sold as an aquarium plant. With severe infestations, EWM halts all forms of recreation on bodies of water due to the dense mats it forms in the water. There have even been reported deaths due to drowning affiliated with this plant. Any fragment of this plant can remain dried for up to seven days and once it hits water, will become viable and spread.

Commonly Confused Plants

  • Coontail
[caption id="attachment_55" align="aligncenter" width="300"]native vs water milfoil Native Milfoil (left) vs. Eurasian Water Milfoil (right)[/caption]

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Photo credits:Nina Eckberg, Thomas Woolf, Heidi Sedivy