Threats to Aquatic Environments - Unwelcome Guests—aquatic Invasive Species

Invasive species can be domestic or foreign. Some aquatic invasive species have been introduced purposely to U.S. waterbodies, for example, to improve sport and recreational fishing. Others have been introduced unintentionally. The primary source of these aquatic invasive species has traditionally been ship ballast water, which is generally picked up in one location and released in another. According to Leo O'Brien, executive director of Baykeeper (a group trying to protect and improve the water quality of the San Francisco Bay/Delta Estuary), it is estimated that a new invasive species becomes established every fourteen weeks through ballast water in the San Francisco Bay alone. Invasive species are also established through transfer from recreational boating vessels; dumping of live bait; release of aquarium species; and accidental escapes from research facilities and aquaculture pens.

The Nonindigenous Aquatic Nuisance Prevention and Control Act of 1990 and the National Invasive Species Act of 1996 are intended to help prevent unintentional introductions of aquatic nuisance species.

Invasive aquatic species include the common carp, bluegill, largemouth bass, smallmouth bass, shad, walleye, and brook trout. The common carp was purposely brought to the United States during the 1800s from Europe. It thrived so well that it soon spread across the country. Today the fish is considered a pest. It competes against native species for food and habitat.

In the state of Georgia, invasive Asian eels have increased in number in many habitats. These species were brought over from Southeast Asia or Australia, where they are considered delicacies. The three-foot-long, flesh-eating eel preys on species such as largemouth bass and crawfish in and around the Chattahoochee River. The eels have gills but can also breathe air—this enables them to worm their way across dry ground to get from one body of water to another. Asian eels have few predators in their new habitat, and humans have found no effective way to control them. As of 2006 three populations of Asian eel had been identified in Florida, confirming fears that the eel would spread beyond Georgia. According to a fact sheet prepared by the Florida Integrated Science Center of the U.S. Geological Survey, one colony was living in canals in the northern Miami area, once colony was near Tampa Bay, and one colony was within a mile of the eastern edge of Everglades National Park.