About Invasive Species

Didymo imageDidymo (Didymosphenia geminata, a.k.a. ‘rock snot’) is a freshwater diatom (a type of algae) that was first observed producing nuisance blooms in rivers of northeastern Canada and the U.S. in 2006.   Though originally native to far northern latitudes of Europe, Asia, and North America, it has undergone a recent large range expansion.   Didymo can produce thick, persistent mats of stalk material that alter aquatic insect communities and threaten the recreational and aesthetic value of infested waters.  The algae are likely being spread by hitchhiking on recreational gear and equipment - of particular concern are felt-soled waders and other absorbent clothing which are difficult to dry or disinfect, and may harbor live didymo cells for many weeks.


The Northeast Aquatic Nuisance Species Panel urges the implementation of spread prevention practices to minimize the spread of didymo and other invasive species.

For recommended spread prevention practices click here.

For additional information about didymo, including distribution of didymo in the northeast, click here


Examples of Aquatic Nuisance Species in the Northeast

zebra mussel imageZebra 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, Quebec, and western Massachusetts. The Massachusetts infestation was discovered in 2009. 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 watermilfoil imageEurasian watermilfoil (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. Eurasian watermilfoil 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. Eurasian watermilfoil 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 Eurasian watermilfoil can restrict swimming, fishing and boating.


Japanese shore crab imageThe 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. The Japanese shore crab 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.