Eurasian Watermilfoil General Information


“Why are there so many weeds in the lake?” you ask. “It wasn’t always like this…”One answer is “Eurasian Watermilfoil Infestation.”

What does Eurasian Watermilfoil look like?

milfoilsmThe Eurasian Watermilfoil, also known by its Latin name Myriophyllum spicatum, is a submerged perennial aquatic plant that has become a major aquatic nuisance throughout much of North America. Plants are rooted at the lake bottom and grow rapidly creating dense beds and thick canopies. They typically grow in water depths of 1 to 4 m, but have also been found growing in water as deep as 10 m.


Feather-like leaves are arranged in whorls of 4 around the stem at each node. Each Eurasian Watermilfoil leaf generally has 12 or more leaflet pairs. The growing stems of Eurasian Watermilfoil are tassel like and often red, especially in the early growing season. In mid-summer it’s thick canopies are dotted with tiny pinkish flowers. milfoil closeup

Where did they come from?

They originated from Europe, Asia, and Northern Africa and were introduced into North America possibly as early as the 1880’s in Chesapeake Bay. But the first inland reports were made in the in the 1940’s. Since that time they have spread rapidly especially with the increase of recreational boating. Plant fragments are easily transported in live wells, bilge water, and on boat motors and trailers. Eurasian Watermilfoil is currently reported in nearly every State in the continental USA.

Why are Eurasian Watermilfoil a problem?

The plants form dense stands of vegetation in the water column and thick mats at the surface, shading out native vegetation and reducing oxygen levels during decomposition. This dense vegetation also takes away from recreational activities. Swimming areas can be taken over and boat propellers become entangled sometimes to the point where the lake is no longer navigable. The stagnant water created by Eurasian Watermilfoil stands provides good breeding grounds for mosquitoes.

How are Eurasian Watermilfoil spread?

Although they do produce seeds, Eurasian Watermilfoil reproduce mostly by fragmentation. The plants naturally fragment during their growth cycle . The fragments develop roots and sink to the lake bottom. Efforts to harvest milfoil by cutting either mechanically or manually may only serve to worsen the problem if the plant fragments are not thoroughly collected. Also boat propellers can sever the plants and cause additional fragmentation.

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What good are native aquatic plants, anyway?

  • Provide habitat for fish, bird, insects
  • Provide shade, shelter & foraging opportunities for fish
  • Photosynthesize which oxygenates the water
  • Stabilize sediments
  • Absorb nutrients
  • Slow down water
  • Can be aesthetically pleasing