Mussel shell button manufacturing peaks at 5.7 billion buttons. Freshwater mussels recovered in a few clean streams where excessive harvesting did not occur. Freshwater mussels are found in the shallow riffles of clean streams, healthy populations today are found in French Creek and the upper reaches of the Allegheny River. They are filter feeders that help keep streams clean by filtering water and removing sediments 24 hours a day for the duration of their long lives--up to 40 years. Mussels are considered "bioindicators;" that is, their presence in streams indicates very good water quality.