Our freshwater native plants, lake plants, are threatened by the invasive eurasian watermilfoil. This plant is quite opportunistic and thrives in lakes where there isn't a lot of native plant life. In those lakes where plants are scarce, eurasian watermilfoil can spread quickly and become very dense. It will choke out the plants that exist there and create a dominated ecosystem that becomes so thick with matted milfoil that boats have difficulty navigating in areas that were once sparsely scattered with plant life.
Eurasian watermilfoil is not easy to identify and can be easily confused for other types of watermilfoil plants. The main thing to remember is that eurasian watermilfoil has whorls of four and is fully submerged. It's threadlike leaves get up to about a half inch long. Where it gets a little confusing is the amount of leaflet pairs. Eurasian watermilfoil will have twice as many leaflet pairs at the northern watermilfoil. Eurasian watermilfoil can grow from just a piece of stem. So, if the plant gets on your motor and you launch in a lake that does not have eurasian watermilfoil, you just put that body of water in jeopardy. Yet, waterbirds such as ducks, geese, herons, and seagulls have played a role in the spread of eurasian watermilfoil. In lakes where the plant has already established itself, it can spread faster to other parts of the lake because motors chop up the plant and carry it across the water. When eurasian watermilfoil is broken apart, it spreads much more rapidly and intensely. There's a moth that actually feeds on eurasian watermilfoil called the water veneer moth. Grass carp also feed on these plants, keeping them in check. But, the grass carp is also an invasive species, so who really wins?
The grass carp eat a variety of plants and often times will prefer the native stuff over the eurasian watermilfoil. Once this plants gets established it is virtually impossible to eliminate it. Harvesting the plant by hand or with machines has proven to be fairly effective in the midwest, but must be done routinely every year to keep the plant in check. Eurasian watermilfoil can greatly impact the economics of your lake in a substantially negative way. Its dense canopies squeeze out other plants and are not very good habitat for wildlife because of how densely they can grow. When out of control, this plant can affect the phosphorus and nitrogen levels in a lake, impacting the overall water quality. It also raises the pH level and reduces the amount of lake oxygen. The temperature of the lake rises and creates a friendly breeding ground for mosquitoes. It can get to the point where the plant is interfering in or eliminating the opportunity for recreational activities. When that happens money has to be spent eradicating or else a lake community will wind up losing tourism dollar. Eurasian watermilfoil must be controlled before severe infestation. In the state of Wisconsin, for example, over a million dollars a year is spent maintaining the spread of this plant.