Eurasian watermilfoil is a dangerous, aggressive, noxious weed that is an invasive species. It invades lakes, ponds, reservoirs, drainage canals and streams throughout the world and in Chicago and Illinois. http://www.illinoiswildflowers.info/wetland/plants/eurmilfoil.html It particularly likes manmade ponds because they have low acidity and are generally located in sunny areas with little shade from trees and shrubs. Still or slow moving water provides an ideal environment for this aquatic plant.
This weed spreads quickly and overruns native plants. It creates massive, dense mats that interfere with boating and water sports. It affects fish spawning and growth. Successful methods to control it can disturb bodies of water, are costly to implement or require manual labor.
Eurasian watermilfoil belongs to the Order Saxifragales, the Family HALORAGACEAE, the Genus Myriophyium and the Species M. spicatum. It has red to olive-green branching stems that can grow to ten feet tall. The submerged leaves are pinnate whorls of four sections and can be up to 1.4 inches in length. Separate female and male flowers grow from the same leaf axils. Male flowers develop at the tips of the flower spike while female flowers form at the base of the spike. These flowers are usually orange-red.
This plant invades every continent except Australia and Antarctica. However, it has been spotted in a few bodies of water in Australia. The first record of this weed appearing in Illinois was in Lake County, Illinois in 1916. Many sightings were recorded in North America in the 1940s. http://www.invasivespeciesinfo.gov By the 1970s, it had invaded thousands of miles in British Columbia and Ontario, Canada.
While Eurasian watermilfoil looks lovely with its feathery foliage, it ruins bodies of water. If you have a pond, remove Eurasian watermilfoil and plant Canadian waterweed (Elodea canadensis), wild celery (Vallisneria americana) or sago palmweed (Potamogeton pectinatus) instead.