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FACT SHEET: EURASIAN WATERMILFOIL

Eurasian Watermilfoil 

Myriophyllum spicatum L. 

Water-milfoil family (Haloragaceae) 

NATIVE RANGE 

Eurasia and Africa 

DESCRIPTION 

Eurasian watermilfoil, also called spike watermilfoil, is an emergent, 

herbaceous aquatic plant. Stems grow to the water surface, usually extending 

3 to 10, but as much as 33, feet in length and frequently forming dense mats. 

Stems of Eurasian milfoil are long, slender, branching, hairless, and become 

leafless toward the base. New plants may emerge from each node (joint) on a stem, and root upon contact with mud. The 

grayish-green leaves of Eurasian watermilfoil are finely divided and occur in whorls of three or four along the stem, with 

12-16 pairs of fine, thin leaflets about 1/2 inch long. These leaflets give milfoil a feathery appearance that is a 

distinguishing feature of the plant. Eurasian watermilfoil produces small yellow, 4-parted flowers on a spike that projects 2-

4 inches above the water surface. The fruit is a hard, segmented capsule containing four seeds. 

ECOLOGICAL THREAT 

Eurasian milfoil can form large, floating mats of vegetation on the surface of lakes, rivers, and other water bodies, 

preventing light penetration for native aquatic plants and impeding water traffic. The plant thrives in areas that have been 

subjected to various kinds of natural and manmade disturbance. 

DISTRIBUTION IN THE UNITED STATES 

Watermilfoil occurs in thirty-three states east of the Mississippi River and has 

recently been found in Colorado. It is abundant in the Chesapeake Bay, the 

tidal Potomac River, and several Tennessee Valley reservoirs. 

HABITAT IN THE UNITED STATES 

Typical habitat for Eurasian watermilfoil includes fresh to brackish water of fish 

ponds, lakes, slow-moving streams, reservoirs, estuaries, and canals.. It is 

tolerant of many water pollutants. Eurasian watermilfoil tends to invade 

disturbed areas where native plants cannot adapt to the alteration. It does not 

spread rapidly into undisturbed areas where native plants are well established. 

By altering waterways, humans have created a new and unnatural niche where milfoil thrives. 

BACKGROUND 

Eurasian watermilfoil was accidentally introduced from Eurasia in the 1940s. Two theories exist as to how it entered North 

America: (1) it escaped from an aquarium, or (2) it was brought in attached to commercial or private boats. A resort owner 

is thought to have introduced watermilfoil into the Tennessee Valley Authority reservoir system in 1953. 

BIOLOGY & SPREAD 

Most regeneration of Eurasian watermilfoil is from rhizomes, fragmented stems, and axillary buds that develop throughout 

the year. Flower spikes often remain above water until pollination is complete, then resubmerge. Although seeds are 

usually viable, they are not an important means of dispersal. 

MANAGEMENT OPTIONS 

Large harvesting equipment can be used to mechanically remove milfoil in larger areas; a sturdy hand-rake can be used 

for smaller areas. Other available options include manipulation of water level, light penetration and chemical control. 

Potential impacts to existing native aquatic plant species should be evaluated carefully before implementing any of these 

techniques. For the single harvest, removal should take place just before peak biomass is obtained (early summer). 
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Substantial regrowth may occur if this is done too early. Better results appear with multiple harvests in the same growing 

season. If multiple harvests are not possible, then sustaining annual harvests is an option. All fragments of milfoil plants 

must be removed to achieve adequate control. 

Where water levels are under manual control, raising or lowering of the water can be an effective way to reduce the 

growth of milfoil. By raising the water level, plants can be "drowned" by not having access to enough light. By lowering the 

water level, plants can be dehydrated and, at the right time of the year, frozen to death. This type of control is best used in

conjunction with herbicides and shade barriers. 

Bankside plantings, floating native plant species, light limiting dyes, or shade barriers are effective ways of reducing the 

amount of light reaching the plants and may reduce overall growth rates. Barriers can be used to prevent the movement 

and spread of aquatic weeds in ponds and lakes. A barrier is usually a suspended blocking screen that hangs vertically 

from a cable to a depth of about 4 meters; the cable is suspended by drum floats. 

Fluridone (the active ingredient in Sonar® AS) is a selective herbicide for milfoil and several other exotic aquatic weeds. 

There are no restrictions on swimming, fishing, or drinking after application, and season-long control can be achieved with 

one application. Fluridone is available in liquid or granular form, and can be used as a spot treatment or on an entire 

waterway. For best results, applications should be made before or during the early stages of active growth. 

USE PESTICIDES WISELY: Always read the entire pesticide label carefully, follow all mixing and application instructions and wear all 

recommended personal protective gear and clothing. Contact your state department of agriculture for any additional pesticide use 

requirements, restrictions or recommendations. 

NOTICE: mention of pesticide products on this page does not constitute endorsement of any material.

CONTACT 

For more information on the management of Eurasian watermilfoil, please contact: 

• Kris Johnson, Great Smoky Mountains National Park, Gatlinburg, TN 

• Al Cofrancesco, U.S. Army Corps of Engineers, cofrana at ex1.wes.army.mil 

• Ken Langeland, University of Florida Institute of Food and Agriculture, kal at gnv.ifas.ufl.edu 

• http://nas.er.usgs.gov/dicots/my_spica.html 

• http://www.des.state.nh.us/wmb/exoticspecies/identify.htm 

SUGGESTED ALTERNATIVE PLANTS 

Yellow nelumbo (Nelumbo lutea), pond weed (Potamogeton nodosus), butterweed (Senecio glabellus) are some 

alternative plants to consider for the eastern U.S. 

OTHER LINKS 

• http://www.invasive.org/search/action.cfm?q=Myriophyllum%20spicatum 

• http://nbii-nin.ciesin.columbia.edu/ipane/icat/browse.do?specieId=78

AUTHORS 

Tom Remaley, Great Smoky Mountains National Park, Gatlinburg, TN 

EDITORS

Jil M. Swearingen, National Park Service, Washington, DC 

Alison A. Dalsimer, Consultant, Legacy Resource Management Program, Washington, DC 

PHOTOGRAPHS 

Barry A. Rice, The Nature Conservancy, Davis, CA 

REFERENCES 

B.C. Ministry of Environment 1989. Eurasian Water Milfoil in British Columbia (Pamphlet). 
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Plant Conservation Alliance®s Alien Plant Working Group 

Xeeds HoneXild: Alien Plant Invaders of Natural Areas 

http://www.nps.gov/plants/alien/

Gleason, H.A., A. Cronquist. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. 2nd ed. 

The New York Botanical Garden, 910. 

Swearingen, J. 2009. WeedUS Database of Plants Invading Natural Areas in the United States: Eurasian Watermilfoil 

(Myriophyllum spicatum). http://www.invasive.org/weedus/subject.html?sub=3055. 

USDA, NRCS. 2009. The PLANTS Database (http://plants.usda.gov). National Plant Data Center, Baton Rouge, LA 

70874-4490 USA.