Eurasian watermilfoil displaces native plant species and decreases the abundance and diversity of aquatic insects and fish. Decaying plant material can decrease oxygen levels, which is a further detriment to fish and other organisms. Large infestations impede water flow and can cause stagnant water conditions that create habitat for mosquitoes and the parasites that cause swimmer’s itch. Large infestations also damage fishing, hunting, boating, and other recreational activities. Eurasian watermilfoil is capable of hybridizing with the native northern watermilfoil (Myriophyllum sibiricum), and some hybrid strains have proven to be even more aggressive.