|Water-milfoil (Myriophyllum spicatum) in Ontario coating the bottom of a body of water.|
|A detailed illustration|
Managing this plant has proven to be difficult, as it always is when dealing with an invasive species. Herbicides have been tried with little success, but more success has been seen using physical methods. Blocking light from the plants and also removing them or chopping them to bits have had at least some success. There has also been a biological control that has been proposed in the form of a species of weevil.
I don't honestly know what else to talk about. There is a lot more reading to be done on this species, especially if your are interested in the structure, distribution, reproductive methods, and so on. Aquatic plants are quite intriguing due to their only distant relationships with algae. Some of the sources I found most informative are the Wisconsin Department of Natural Resources, United States Geological Survey, and University of Florida.
Source is the Global Invasive Species Database. Images are from Wikimedia Commons and are copyright free or under a Creative Commons license: one, two.