The waters of northeastern North America are being transformed by invasive aquatic plants, fish, invertebrates, and other organisms from around the world. These plants and animals, which may be introduced both intentionally and accidentally, can irrevocably alter our native ecosystems. While they may be benign in their own native habitat, once "invaders" are established in a new ecosystem where their common predators do not exist, they can harm native species by eating their food, preying on them, transmitting diseases to which native species have no defense, or (like many invasive aquatic plants), simply outgrowing them. Not all non-native species cause serious problems, but some do, disrupting entire ecosystems by destroying habitat and altering food chains. These plants and animals are known as aquatic nuisance species or ANS. ANS not only threaten the natural environment, they also cause serious economic damage. Each year in North America, federal, state, and provincial governments, utilities, and businesses spend billions of dollars attempting to prevent, control or slow the spread of these plants and animals. Recreational activities are negatively affected when invasive plants choke fishing, boating, and swimming areas, and human health can also be threatened, as some aquatic nuisance species carry disease or parasites.

Some Examples of Aquatic Nuisance Species in the Northeast
Zebra mussels (Dreissena polymorpha) and "quagga mussels" (Dreissena bugensis) were introduced into North America in freshwater ballast from international shipping. The mussels are natives of the Black, Caspian and Aral Seas of Eastern Europe and Western Asia. Since their 1988 discovery in the Great Lakes, the mussels have spread throughout the Great Lakes and many navigable rivers and are now found in 21 states and two provinces. The easternmost sightings of the mussels are in New York (including the Hudson and St. Lawrence Rivers and Lake Champlain), Vermont, Connecticut and Quebec. The mussels could spread east by "hitchhiking" on recreational boats trailered from lake to lake or by commercial bait and hatchery stocking activities and in anglers' bait bucket water. Zebra mussels are voracious filter feeders; each adult mussel can filter up to 2 quarts of water per day, removing microscopic plants and animals from the water and impacting the natural aquatic food chain. This could result in fewer fish of all kinds, particularly sportfish such as trout, salmon, and bass. The mussels also clog power plant, industrial, and public drinking water intakes, foul boat hulls, and litter bathing beaches. Economic impacts of the mussels are expected to be in the billions of dollars.

Eurasian Water Milfoil (Myriophyllum spicatum) is a submersed, rooted plant that is native of Europe, Asia, and northern Africa. Since its introduction in the 1940's, it has spread to 45 states and three Canadian provinces. M. spicatum is expanding throughout northeastern New York, particularly the Upper Hudson River region and into the Adirondacks. It has been reported in more than 45 lakes in Vermont, mostly in the western part of the state, including Lake Champlain, and is found in New Hampshire waters of the Connecticut River. Locally abundant infestations are found in Massachusetts, Connecticut and Rhode Island. M. spicatum has also been found in Maine, British Columbia, and Quebec. It competes aggressively, displacing native plants and reducing biodiversity. The plant has little value as food for waterfowl, and it reduces the abundance and diversity of invertebrate fish food. Dense beds of M. spicatum can restrict swimming, fishing and boating.

The Japanese shore crab (Hemigrapsis sanguineus) is a small (2 to 3 inch) crab, native to Japan and the western North Pacific, which was released from ballast water in New Jersey around 1987. The crab has spread from Maine to North Carolina, and has become the dominant crab species in the rocky intertidal zone of the Northeast. Hemigrapsus is omnivorous (it will eat plants and animals), and has an appetite for young clams, mussels, oysters, algae, fish larvae, and many other species. The crabs may threaten ecosystems and aquaculture in the Northeast.