Major threats to mussels include loss of habitat (from channel modifications, dams, etc.) and habitat deterioration from pollution. Other threats are the introduction of nonindigenous species and poaching for commercial trade.
Unionacea has a worldwide distribution with the greatest diversity occuring in north America, chiefly east of the Mississippi River, but with a few species established along the Pacific Coast. Typically found in streams, some species may be found in ponds or lakes. In order to reproduce, they require a stable, reasonably undisturbed habitat of clean water. Fish of particular species are required as hosts for mussel larval development. After fertilization and development within the female mussel, the larvae are released and attach themselves to fish hosts. The larvae mature further, drop off the host, and settle into the stream bottom.
Little concern, however, has been generated due to lack of knowledge and public appeal. Freshwater mussels serve many purposes, including indicators of water quality. The importance of native freshwater mussels is gradually being recognized through education, research, and conservation. Recent conservation efforts focus on the restoration of mussel habitats and the controversial reintroduction of native species.
There are approximately 300 recognized species of native freshwater mussels Unionids in the United States, of these 18 are thought to be extinct, nearly 60 listed as "endangered" or "threatened" and 58 listed as candidates for protection under the Endangered Species Act (USA).