Rivers are high-speed corridors for the spread of invasive exotic plants. Increasingly, these plants are pushing out native species and making floods more likely. A study conducted by Deltares, Utrecht University, Radboud University and the German Institute for Flood Plain Ecology has shown that exotic varieties like the Japanese knotweed and the Himalayan balsam grow faster and form denser vegetation in European flood plains than the native vegetation. The phenomenon is also seen Dutch river areas.