Native aquatic plants have existed for approximately as long as there have been aquatic environments, usually in reasonable equilibrium with the lakes and streams supporting them. Nonnative plants are frequently introduced into U.S. waters. Lacking the biological and climatological constraints that may have existed in their native habitats, and nourished by the high nutrient effluents currently encountered in most local waters, these noxious plants often spread prolifically. Their unchecked growth causes not only displacement of native plant species, but substantial takeover of previously open water in reservoirs and waterways. This diminishes the free flow of water, reduces recreational potential and property values, increases transpiration losses, restricts navigation, increases water treatment costs, and provides ideal breeding grounds for disease vectors.