Eurasian Watermilfoil
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About This Species
Eurasian watermilfoil is not native to Colorado. It is a highly aggressive species that can survive in a variety of habitats and grows and average of 1 foot per week. These dense mats crowd out native species, disrupt the food chain and displace native wildlife. It also impedes water recreation such as boating, swimming and fishing.
More Information:
Physical Characteristics
Eurasian watermilfoil is a submerged, rooted perennial with long, branching stems and soft feathery leaves attached in whorls of four.
Leaves
Each leaf has 11 to 21 pairs of leaflets, which are closely spaced, and about ½ inch long.
Flowers
Eurasian watermilfoil produces small yellow, four‐parted flowers on a spike that projects two to four inches above the water surface.
Commonly Found
Eurasian watermilfoil (EWM) is native to Europe, Asia and Northern Africa. It was most likely introduced through the nursery trade in the 1940’s, but possibly as early as the late 1880’s.
Range
It is not widespread in Colorado. Most locations are on the front range from Fort Collins to Pueblo. The only two locations on the west slope are in the Rio Grande and Navajo Res in the SW. The majority of the west slope and eastern plains are free of this invader for now!
Habitat
Tolerates a wide range of water conditions and depths; prefers nutrient‐rich substrate.
Reproduction
Eurasian watermilfoil reproduces by seeds, fragmentation, and winter buds. Fragmentation and winter buds are believed to be more important in spreading the plant. Any plant fragment can start a new infestation. Winter buds are tight leaf clusters that break off and fall to the bottom, where they overwinter. In the spring, the buds grow and form new plants.
Threats to Species
Eurasian watermilfoil forms dense mats that restrict swimming, fishing, and boating and clog water intakes. The mat alters water chemistry by choking and shading out other native aquatic plants. The decaying plants decrease oxygen levels in the water and foul lakeside beaches. This disrupts the food chain and destroys habitat and food needed by fish and birds. Eurasian watermilfoil slows the flow of water in irrigation ditches and canals and creates standing water that is ideal mosquito habitat.