Freshwater mussels, also called bivalves, are members of the mollusk family. They are important animals that live buried in the bottoms of West Virginia's streams and rivers.

They have a hard outer shell (two halves called valves) and a soft inner body with a large, muscular "foot" they use to move. Mussels feed by filtering algae and tiny debris from the water. Because they filter pollutants, their health tells us if the water is clean.

Prehistoric people used them for food and tools. More recently, their shells have been used to make buttons and are now used to grow cultured pearls.

Freshwater mussels are one of the most endangered animal groups in North America. West Virginia has five species listed on the federal Endangered Species List.

Mussels need a fish host to complete their life cycle, which helps them move and spread to new areas. Dams block fish movement and destroy the shallow, fast-moving water areas (riffle habitat) that mussels need. Pollution, such as acid mine drainage, has almost wiped them out in some areas, such as the Monongahela River.

The zebra mussel (introduced from Europe) is an invasive species that clogs water pipes and competes with native mussels, though it has caused less damage than expected in West Virginia.