Southwestern Pennsylvania is seeing a surprising number of freshwater mussel species return to waterways, experts found after concerted efforts to improve habitat and reintroduce declining species. None of the mussel species found is endangered. Of its 67 freshwater mussel species, 12 are considered endangered or threatened at the state or federal level. But historically, it was the most diverse river in the entire state, and it had 53 species,” Welte said. The state Fish and Boat Commission is also raising and releasing eight species of mussels.