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photo courtesy Biosecurity, Division of the Ministry of Agriculture and Forestry, New Zealand

What is Eurasian Watermilfoil?

Weed or water plant, whatever you call it, Eurasian Watermilfoil, also called spiked milfoil, is trouble spelled with a capital “T”, and once established, is difficult if not impossible to eradicate.

Native to Europe, Asia, and northern Africa, this submerged menace, is now widespread throughout much of the United States, threatening waterways from Washinton state to Florida, and from Texas to Maine.

This attractive, feathery plant, once a favorite of homeowner tropical fish tanks, and sold indiscriminately by pet stores throughout the country, literally strangles life from its host.

Its arrival and results are devastating; milfoil reproduces rapidly and can infest a water body in as short a period as two years, turning a healthy vibrant lake, pond or river into an un-traversable swamp.

“Eurasian watermilfoil adversely impacts aquatic ecosystems by forming dense canopies that often shade out native vegetation. Monospecific stands of Eurasian watermilfoil provide poor habitat for waterfowl, fish, and other wildlife. Significant rates of plant sloughing and leaf turnover, as well as the decomposition of high biomass at the end of the growing season, increase the internal loading of phosphorus and nitrogen to the water column. Dense Eurasian watermilfoil mats alter water quality by raising pH, decreasing oxygen under the mats, and increasing temperature...Stagnant water created by Eurasian watermilfoil mats provides good breeding grounds for mosquitoes... In Washington, private and government sources spend about $1,000,000 per year on Eurasian watermilfoil control. Other states and provinces (Minnesota, Wisconsin, Vermont, New York, and British Columbia) spend similar amounts per year to control Eurasian watermilfoil infestations...”
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The Invader

Perennial, aquatic, water plant introduced from Eurasia, probably in the 1940s.

Preferred habitat: Fresh or brackish water of fishponds, lakes, slow-moving streams, reservoirs, and canals. Dispersal is primarily by fragmentation.

Height: Normally between 3 and 10 feet, but can extend up to 33 feet.

Stems: Long and slender, growing to the surface of the water, often forming dense mats. Each floating node can become established if it comes in contact with mud.

Leaves: Grayish- green color in whorls of three or four with 12-16 pairs of fine, thin leaflets up to 1.4 inches in length.

Flowers: Yellow flowers are on a spike that is produced 2-4 inches above the water surface.

Blooms: July-September

Seeds: Fruit is a schizocarp containing four seeds. Matures late July-September.

Manner of distribution: Plant fragments can attach to objects in the water such as boats, trailers, or animals and be moved from one body of water to another.