Hydrilla verticillata was imported from Sri Lanka in the 1950s first to St. Louis and used as a popular aquarium plant. Hydrilla is rooted but concentrates 70% of its biomass at the surface forming a dense canopy during summer and early fall growing to depths of 15 meters. It can reproduce when detached stem fragments readily develop into new plants and attach to the soil.  Recreational boating is the most common method for the spread of this plant now. Hydrilla can alter ecosystems by shading out native submersed vegetation. The production of allelopathens by Hydrilla has been shown to negatively affect the distribution of at least one native plant here in Florida, Ceratophyllum demersum.  Researchers have reported changes in lake water chemistry after the introduction of Hydrilla in many lakes. An obvious and important impact on fish communities occurs here when open water feeding is not longer possible.