In areas of North America where hydrilla has become established, hydrilla has major detrimental impacts on water use. Hydrilla adversely affects aquatic ecosystems by forming dense canopies that often shade out native vegetation. Extensive monospecific stands of hydrilla can provide poor habitat for fish and other wildlife, although hydrilla is eaten by waterfowl and is considered an important food source by some biologists. While dense vegetation may contain large numbers of fish, density levels obtained by plant species such as hydrilla may support few or no harvestable-sized sport fishes. Dense mats alter water quality by raising pH, decreasing oxygen under the mats, and increasing temperature.
Stagnant water created by hydrilla mats provides good breeding grounds for mosquitoes.
Hydrilla interferes with recreational activities such as swimming, boating, fishing and water skiing. In the Western states, hydrilla has the potential to impact power generation, irrigation, and water delivery systems by clogging dam trash racks and intake pipes. In areas where hydrilla, Eurasian watermilfoil, and Brazilian elodea coexist, hydrilla outcompetes these other two noxious species. Hydrilla has the potential to cause greater adverse impacts to aquatic ecosystems than either Eurasian watermilfoil or Brazilian elodea, both severe problem species in some Western states. In states where hydrilla has become established, millions of dollars are spent each year for management activities.