Native to parts of Europe, Asia and north Africa, watermilfoil came to America in the 1940s as an aquarium plant. At some point, someone introduced this plant into a local waterway, and it has spread to every state in the U.S. by hitchhiking on boats. Until 2007, only Montana and Wyoming were believed to not have a Eurasian watermilfoil infestation.
The Noxon Reservoir in Montana has become overgrown with Eurasian watermilfoil in the past several years. Several problems have developed as a result of it being so thick and overgrown. Boat propellers and intake pipes become clogged. Fish can end up dead, smelling in the hot sun, after becoming entangled in mats of the watermilfoil. Oxygen in the water is decreased, and the food chain and pH have changed. Swimmers have even drowned. Unfortunately, this plant is thought to be impossible to eradicate. Billions of dollars have been spent in the United States trying to get rid of it, but it seems to be a losing battle.