Eurasian watermilfoil (Myriophyllum spicatum):

Eurasian watermilfoil is a plant with long branching stems that produce many whorls of finely divided leaves. Similar to other invasive species, it forms dense mats and interferes with recreation, navigation and water flow. A native of Europe, Asia and Northern Africa, Eurasian watermilfoil is now one of the most widely distributed invasives in the US, found in all but five states (Alaska, Hawaii, Maine, Montana and Wyoming). The most common means of control are herbicides and mechanical harvesting.