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Eurasian watermilfoil Credit: RIDEM K. DeGoosh

Eurasian watermilfoil
Myriophyllum spicatum

History:

• Introduced to the United States in the 1940s

Characteristics:

• Rooted, submersed, perennial, aquatic plant
• Narrow, whitish stems grow to the water surface, extending 3-10 ft (1-3 m) or longer
• Forms dense beds
• Feather-like leaves with blunt ends commonly with 12 to 24 pairs of leaflets on each leaf
• Leaves are grouped in whorls of 3 - 6 leaves around stem
• Small flowers project 2-4 in (5-10 cm) above the water surface

Habitat:

• Lakes, ponds, slow-moving streams, reservoirs, and estuaries
• Depths greater than 3 ft (0.9 m)
• Tolerates brackish water
• Thrives in highly disturbed lake beds, lakes receiving nitrogen and phosphorus-laden runoff, and heavily used lakes

Known Distribution:

• Quebec and most of the U.S. 
• Native to Europe and Asia

Impacts:

• Highly aggressive, nuisance species
• Can form dense mats that shade and crowd out native plants
• Degrades habitats used by fish for spawning and feeding
• Thick growth can impair recreational uses of waterways including boating, swimming, and fishing
• Yellow-green, matted vegetation on milfoil-dominated lakes creates perception that lake is “infested” or “dead"
• Control efforts cost millions of dollars annually; $500,000 per year in New York state alone

Common Vector(s):
Overland transport (e.g. boats, equipment)

Eurasian watermilfoil underwater

Eurasian watermilfoil leaves Credit: MEDEP-K.Hahnel

Eurasian watermilfoil Credit: RIDEM - K.DeGoosh

Eurasian watermilfoil (Myriophyllum spicatum) Credit: Alison Fox, University of Florida

Eurasian watermilfoil-leaves whorled around stem Credit: MEDEP - K.Hahnel