• Accidentally introduced to northeastern United States sometime between the late 1800s and 1940s

• Rooted, submersed, perennial, aquatic plant
• Narrow, reddish-brown stems grow to the water surface, extending 3-10 ft (1-3 m) or longer
• Forms dense beds
• Feather-like leaves with blunt ends, grouped in whorls around stem
• Small flowers project 2-4 in (5-10 cm) above the water surface

• 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

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

• 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