[www.invasive.org] Central Africa native, Ecological threat: Origin: Central Africa Background Hydrilla first appeared in the Crystal River system of Florida in 1960. Imported by the aquarium trade, its presence on the Delmarva Peninsula was confirmed in 1981. It attracted national attention when infestations were found in the Potomac River in Washington, D.C. in the early 1980s. It is a federal noxious weed. Distribution and Habitat Hydrilla is documented throughout the southern United States from California to Delaware. In the mid-Atlantic, it occurs in much of the Potomac River, in Virginia and Maryland freshwater tributaries of the Chesapeake Bay, in the Delaware portion of the Nanticoke River, most southern Delaware ponds, and in sites in eastern Pennsylvania. It is not salt tolerant. Ecological Threat Hydrilla outcompetes native submerged aquatic vegetation and can quickly fill a pond or lake, thus choking off the water body for boating, fishing, swimming and other recreational uses. Although non-native and invasive, it provides good quality habitat for fish and shellfish as well as water quality benefits. (link added by Mary Ann Machi)