Myriophyllum spicatum

Eurasian Watermilfoil is an aquatic plant that was accidentally introduced to the North American east coast from Europe in the 1940's. It has spread westward to inland lakes by boats and water birds. Besides crowding out native water plants, it forms thick mats of vegetation that can interfere with swimming, boating and fishing.

The Eurasian Watermilfoil can be identified from the 12 to 21 pairs of feathery leaflets. Our native northern watermilfoil typically has 5 to 9 pairs of leaflets. Both species are found in water less than 20 feet deep. Milfoil can reproduce from stem fragments and runners. When the plant becomes entangled in boat propellers, or attaches to keels or rudders, or boat trailers, it is spread from lake to lake. The mechanical clearing of aquatic plants for beaches, docks, landings, and swimming areas creates a perfect habitat for this invasive species. It has trouble establishing in areas where there are healthy populations of native species.

Eradicating established populations of Eurasian Watermilfoil is almost impossible. Suppression is through beetles that eat the plants and herbicides that kill off much of the mat-forming foliage.

more info: http://fwcb.cfans.umn.edu/research/milfoil/milfoilbc/milfoil.html