Hydrilla is an aquatic plant that has earned the illustrious title “world’s worst invasive aquatic plant”. Listed as a federal noxious weed, hydrilla has made its home in just about every conceivable freshwater habitat including: rivers, streams, lakes, ponds, marshes, canals, ditches and reservoirs.
Hydrilla was first discovered in the United States in the 1960s in Florida. Since then, it has spread to many parts of the U.S.
Hydrilla can grow in a wide variety of water conditions (e.g., high/low nutrients, high/low turbidity, variable pH, up to 7% salinity) and water temperatures. Unlike most native aquatic plants, hydrilla is capable of growing under extremely low light conditions. Hydrilla is able to begin photosynthesizing much earlier in the morning than native plants so it is able to capture most of the carbon dioxide in the water (which limits growth of other plants). Hydrilla grows very rapidly (it can double its biomass every two weeks in summer) and has no natural predators or diseases to limit its population.
Dense infestations of hydrilla can shade or crowd out all other native aquatic plants, alter water chemistry, cause dramatic swings in dissolved oxygen levels, increase water temperatures, and affect the diversity and abundance of fish populations.
(Via the U.S. Fish and Wildlife Service)