Eurasian Water-Milfoil

History
Eurasian water-milfoil (Myriophyllum spicatum) is a submerged, rooted perennial plant. It has long underwater stems with finely-divided leaves that float near the surface.  The Eurasian species closely resembles Myriophyllum species native to the U.S. but  have more triangular-shaped leaves with more than 14 pairs of leaflets.  The species was introduced in 1942 when it was intentionally planted in ponds of Washington, D.C.

Threat
The species often occurs in high abundance and replaces native plant species.  Rapid colonization can result not only in the disruption of native plant communities but also can change the substrate, water flow patterns and invertebrate communities of an aquatic ecosystem.  Although subsequent impacts to fish populations are poorly known, it is likely they are significant. 

Management Implications
Eurasian water-milfoil occurs in lakes, ponds, shallow reservoirs and low gradient stretches of rivers.  The species has been documented in all states except Montana, Wyoming, Alaska and Hawaii.  It is expanding through much of the Northeast, including the Upper Hudson drainage (NY), numerous lakes (ME & VT), and the Connecticut and Delaware river drainages.  The species also has been documented from the Pend Oreille River and Hayden Lake (ID) and Devils Lake (OR).  Eurasian water-milfoil is easily spread by motorboat traffic (plant fragments can reestablish downstream) and by trailoring boats from one water body to another.  Road checks in Minnesota found aquatic plants on 23% of all watercraft inspected. 

Source: U.S. Geological Survey Nonindigenous Aquatic Species Website http://nas.er.usgs.gov/taxgroup/plants/docs/my_spica.html