Eurasian watermilfoil: A Truly Noxious Plant
"Eurasian watermilfoil (Myriophyllum spicatum) is an attractive plant with feathery underwater foliage. It was once commonly sold as an aquarium plant. Eurasian watermilfoil, hereafter called milfoil, originates from Europe and Asia, but was introduced to North America many years ago and is now found over much of the United States. This plant was introduced to the eastern United States at least as long ago as the 1940s, but it may have arrived as early as the late 1800s. The first known herbarium specimen of milfoil in Washington was collected from Lake Meridian near Seattle in 1965. By the mid 1970s it was also found in Lake Washington. During this same time period milfoil became established in central British Columbia and traveled downstream to Lake Osoyoos and the Okanogan River in central Washington. Now milfoil is found in the Columbia, Okanogan, Snake, and Pend Oreille Rivers and in many nearby lakes. In western Washington, the distribution of milfoil closely follows the Interstate 5 corridor (follow this link to see where it is located in Washington). It is very apparent that milfoil has been spread from lake to lake on boat trailers."
And this warning:
"Because it is widely distributed and difficult to control, milfoil is considered to be the most problematic plant in Washington. The introduction of milfoil can drastically alter a waterbody's ecology. Milfoil forms very dense mats of vegetation on the surface of the water. These mats interfere with recreational activities such as swimming, fishing, water skiing, and boating. In eastern Washington milfoil interferes with power generation and irrigation by clogging water intakes."
And it is nearly impossible to get rid of.