You should have a pretty good idea of what your species needs in its environment to be healthy and vibrant. Do you know if your watershed is healthy for your species?
Freshwater mussels have a unique and complex life cycle involving parasitic larvae. Most of these mussel species have separate sexes, though some species have both male and female reproductive parts. The male ejects sperm into the water which is taken in by the female where it fertilizes the eggs. These fertilized eggs move from the gonads to the gills of the mussel, where they further metamorph into "glochidia", the first larval stage.
Once the glochidia are mature enough, the female releases them into the water where they attach to the gills, fins, or skin of a host fish. The glochidia feed off of the tissue of the fish for several weeks or months before they fall off as juvenile freshwater mussels and then bury themselves in the sediment. This unique life cycle allows freshwater mussels to move upstream with the fish host species.
Mussels are filter feeders, which means they suck in water through the siphon that sticks out of their shell, filter that water to extract the nutrients they need to survive, and then pump the filtered water back out through another siphon. It's estimated that one mussel filters as much as a bathtub of water per day in order to get the nutrients it needs to survive. As such prolific filters, freshwater mussels play an important role in maintaining water quality and clarity. It also means they're extra sensitive to whatever is suspended in that water.
In order to thrive, freshwater mussels like cool, flowing water and a relatively sandy or rocky bottom so they don't bury their siphons in the mud. Though we don't really think of mussels as being mobile, species that have particular host fish that spawn up upriver also require unobstructed rivers to complete their natural range.