Mussels comprise a very important and diverse segment of freshwater stream ecosystems in the United States. Approximately 300 different species and subspecies of freshwater mussels are native to North America, and more than 70% are categorized as endangered, theatened, or of special concern. As filter-feeding animals, they are important biological indicators of the health of aquatic ecosystems. Because each species requires a host fish as part of their life cycle, mussels are both directly and indirectly susceptible to changes in their environment.