Eurasian Watermilfoil

Myriophyllum spicatum

Eurasian Watermilfoil

Family: Haloragaceae

Other Common Names: spike watermilfoil
Weed class: B
Year Listed: 1988
Native to: Europe, Asia and Northern Africa
Is this Weed Toxic?:

not known to be

Legal listings:

WA Quarantine list, WAC 16-752

Why Is It a Noxious Weed?

It is an ornamental aquatic plant that has escaped cultivation. Infestations can alter aquatic ecosystems. It forms dense mats that shade out other aquatic plants, degrades water quality, inhibits water flow and impacts recreational activities.

How would I identify it?

General Description

Eurasian watermilfoil is a perennial, submersed, aquatic plant with dissected leaves. It forms dense mats with flowering stems extending above the water’s surface. There is a land form of the plant that has smaller, stiffer leaves

Flower Description

Flowers are tiny, pinkish and occur on reddish spikes. Male and female flowers are on the same plant.

Leaf description

Leaves are finely dissected and occur in whorls of 4 (rarely 5). Each leaf has 12 or more leaflet pairs (sometimes down to 5 pairs of leaflets). Leaves have a feather-like appearance.

Stem description

Stem tips are tassel-like and often red. They mostly branch near the water's surface. Stems easily fragment.

Fruit Seed Description

Seeds detach from plant, float and then sink if still in water.

Where does it grow?

It is highly adaptable and is found in streams, ponds, lakes and ditches. Please click here to see a county level distribution map of Eurasian watermilfoil in Washington.

How Does it Reproduce?

Eurasian watermilfoil spreads mainly by stem fragments.

How Do I Control It?

General Control Strategy

Eurasian watermilfoil control can be difficult. Since it spreads by stem fragments, care must be taken to ensure the entire plant is removed when mechanical methods or hand pulling is used.

Mechanical Control

Mechanical control is not advised unless the area is entirely invaded by plants. Otherwise, mechanical methods may increase the infestation. Hand pulling may be employed, but the entire plant must be removed or it will re-sprout.

Cultural Control

Small infestations may be able to be controlled with the use of an opaque fabric that blocks light from the plant.

Biological Control

Triploid grass carp will eat Eurasian watermilfoil, but it is not very palatable and is not the preferred food for grass carp. Other biological methods are being researched.

Herbicide Control

Because herbicide availability and regulation differ between states, we recommend the Washington Department of Ecology website for information on aquatic weed management and herbicides, or contact your county noxious weed coordinator.

For More Information

See our Written Findings for more information about Eurasian watermilfoil (Myriophyllum spicatum).

Asotin County NWCB Fact Sheet on Eurasian watermilfoil

Clallam County NWCB Fact Sheet on Eurasian watermilfoil

Jefferson County NWCB Fact Sheet on Eurasian watermilfoil

Lincoln County NWCB Fact Sheet on Eurasian watermilfoil

Whatcom  County NWCB Fact Sheet on Eurasian watermilfoil

Control Options for variable-leaf milfoil and Eurasian watermilfoil from King County NWCB

Additional Photos