Some problems aren't new. Although water quality has improved in some areas, pollution, especially non-point source pollution, causes the greatest threat to native mussels. Also sedimentation continues to take a serious toll. Habitat losses through channelization, clearing of riparian and streambank vegetation, dredging, and dam construction still persist. Mussels are impacted by loss of fish hosts from fish kills or dams that prevent fish migration.
Poachers can impact mussles by violating harvest regulations set by conservation agencies.
However, in some parts of the country, it's a non-native mussel causing the most concern. In 1988, the fist zebra mussels were spotted in Lake St. Claire near Lake Erie in Ohio. Assumed to have been stowaways in the ballast water of a trans-Atlantic ship, this native of eastern Europe is now widespread throughout waterways in the eastern half of the United States. Besides other problems, zebra mussels have nearly eliminated native mussels in some locations. They can attach themselves to hard surfaces with thread-like structures called byssal threads.