Freshwater mussels are members of the mollusk family Unionidae. They have a hard outer covering consisting of two halves, or valves, and a soft inner body. They are not true mussels and are more appropriately called bivalves. Native bivalves possess a large muscular "foot" that is used for locomotion.

Native Americans used these animals for food and the shells for ornamentation and tools. More recently shells were used for the making of buttons, but by the 1940s shell was replaced by plastic. Today shells are used to produce nuclei for the cultured pearl industry. West Virginia does not allow the commercial harvest of freshwater mussels.

There are 60 species of Unionids native to West Virginia, occurring in all parts of the state. They live a fairly sedentary life buried in the stream bottom, where they feed by filtering algae and other organic debris from the water. As a result, they also filter pollutants, and their health provides a sensitive environmental indicator.

Freshwater mussels are probably the most endangered group of animals in North America. Two species of freshwater mussels found in West Virginia, the sheepnose and the spectaclecase, are listed on the federal Endangered Species List.

The Monongahela River watershed, except for a few tributaries, is almost devoid of native bivalves due to acid mine drainage. These bivalves require a fish host for completion of their life cycle, and fish carry them into new areas or to areas previously occupied. Construction of dams eliminates valuable riffle habitat and also inhibits fish movements.

Though no true mussels are native to West Virginia, zebra mussels were introduced from Europe into the Great Lakes by commercial barge traffic about 1986. Currently they are found in the navigable portions of the Ohio, Kanawha, and Monongahela rivers in West Virginia. Zebra mussels can cause great economic losses since they clog water intake pipes, and they represent a serious competitor and threat to native species. West Virginia naturalists expected the worst as zebra mussels spread rapidly through the state's waters in the 1990s, but the creatures have not caused as much damage as expected. Experts say zebra mussels in the Ohio River basin are smaller and easier for predators to harvest, which may help explain why they are less troublesome in the state’s waterways.