Invasive Species on the Potomac River

The Potomac River hosts a number of non native aquatic species of plants and animals. While not all introduced species are necessarily an environmental disaster, there can still be unpredictable consequences resulting from their introduction.

Many of these species such as the Red Swamp Crayfish and the Asiatic Clam are edible and might well have become an economically exploitable resource were it not for the fact that sediments of the Potomac and some of its tributaries such as the Occoquan and Anacostia river are heavily contaminated with PCBs (poly chlorinated byphenols).

Red Swamp Crayfish

Procambarus clarkii

The red swamp crayfish is aggressive and easily out competes native species of crayfish throught the Potomac River Basin.

Also known as the Louisana Swamp crayfish, this species can grow to over 5 inches in length and is commonly farmed in the southern states. Used for Crawfish boils, fishbait . Native to the South Eastern united states and Northern Mexico it can now be found throughout the U.S., Europe1 and some places in Asia 2.

Japanese Mystery Snail

Bellamya japonica

Snail shells of Bellamya japonica. Mason Neck State Park

Live bearing (viviparids) instead of laying eggs miniature snails are released. Growing to 1 1/2 to 2 inches long these asian snails outsize just about all native freshwater snails. They primarily graze on algae and will feed on carrion as well.

Asiatic Clam

Corbicula fluminea

Native to asia, it is thought to have been introduced into North America in the early 20th century. Average size is 1 to 1 1/2 inches long. An edible species of freshwater clam it may have been orginally been imported as food. The asiatic clam is found throughout the potomac river and in many of its tributaries. It requires relatively clean water and it will not survive in water temperatures below 36 degrees fahrenheit. It can be very prolific creating population densities greater than 10,000 clams per square meter. While the asiatic clam is an active filter feeder which can improve water clarity, frequent mass die offs of this creature can severely impact water quality at least temporarily.


Hydrilla verticillata

First identified in the Potomac River in 1982, Hydrilla has spread through much of the South Eastern United States This plant is native to Southeast Asia and is thought to have been first imported to Florida to be sold as a plant for aquariums. It tends to crowd out all other aquatic vegetation.

Eurasian Water-milfoil

Myriophyllum spicatum

Eurasian Water-milfoil is native to Europe, Asia and North Africa. It can form dense mats that shade out more desirable submerged aquatic vegetation. Unfortunately it seems to be unpalatable to most wildlife. Even grass carp will consume all native aquatic vegetation before they will consume this species.

Northern Snakehead

Channa argus

Northern Snakehead Fish- U.S.Geological Survey

Native to China where it is a common food item. The Northern Snakehead is well adapted to survival in polluted environments with low disolved oxygen levels.

About Watershed Conservation Site Index

1. Viet News - Eyes on Vietnam Sep 14, 2010 "Red swamp crayfish escape" Accessed April 27, 2011
2. Food and Agriculture Organization of the United Nations. (n.d.). "Species Fact Sheets - Procambarus clarkii." In FAO Fisheries & Aquaculture. Accessed April 27, 2011, from