Eurasian watermilfoil is a submersed perennial plant that has fine feather-like leaves. These leaves are arranged in whorls of four. The leaf generally has 12 or more leaflet pairs (not to be confused with the native plant Northern watermilfoil that has under 12 leaflet pairs).
This invasive aquatic noxious weed forms very dense thick mats of vegetation on the water's surface. This interferes with water-based recreation such as fishing, boating, water skiing and swimming. The dense mats increase the pH of the water and reduce the amount of oxygen in it killing fish and other life. This destroys water quality and creates a breeding ground for mosquitoes. Swimmers have been known to become entangled and drown in these dense thick mats.
Although Eurasian watermilfoil can spread from seed, it primarily spreads through a process called "fragmentation," where a piece of the plant the size of a small postage stamp breaks off and can start a new infestation. Eurasian watermilfoil is Idaho's only listed aquatic noxious weed. It is a native of Europe, Asia and Northern Africa. It was introduced into the United States in the late 1800's through the Aquarium Trade.
