Eurasian milfoil (Myriophyllum spicatum L.) is a submersed aquatic herb preferring water about 1 to 3 meters deep, although this primarily depends on the depth to which light can penetrate the lake. Its stems can “top out” in 20 feet of water, but the plant is most often found in water 0.5 to 3.5 m deep (Aiken et al. 1979) . It has a smooth stem that is leafless towards the base and branches near the water surface, growing tassel-like and often red apices, especially early in the growing season. The leaves are 1.5 to 4.0 cm long and whorled, usually with four in each whorl. The leaves outline is feather-like. In reproduction stems release fragments that float, develop roots, and new stems and leaves, before sinking and adhering to the bottom substrate. Eurasian milfoil reproduces via cross-pollination. Its’ fruits are 2 – 3 mm long often occurring in bunches.
Humans can spread the plant between water body systems from boats and boat trailers carrying the plant fragments.
There are a number of water-milfoils in the U.S. and Canada, both native and non-native. This species, Eurasian water-milfoil, is the most troublesome of the non-native water-milfoils. While it occurs in almost every U.S. state, it is especially weedy and the subject of much control effort, in the northern tier of states and in Canada, where it fills recreation and fishing lakes, interferes with wildlife and degrades water quality. It often forms large infestations; often is the most abundant submersed species in a locale and spreads and reproduces mainly by regrowth of plant fragments. It will spread to the point where it will halt boat traffic on lakes and rivers and can fill a lake surface from shore to shore.