Mussels are filter feeders, sucking in water and food through specialized structures called siphons. Because they are filter feeders, mussels are especially sensitive to any pollutants within the water. For example, if a barrel of oil spills into a creek, the mussels downstream will eventually take the oil into their bodies. Of the 27 species of mussels found in the French Creek watershed, the Northern Riffle Shell and Clubshell are listed as Endangered. Also, 18 of the species of mussels in French Creek are very rare and are currently being watched carefully.

Because mussels are filter feeders, they do not have to move around to catch their food. Thus, mussels remain relatively stationary. A retractable appendage called a muscular foot is responsible for the mussel's movement. When a mussel feels it's in danger, the foot is quickly retracted within the shell to protect itself from predators. The mussel reproductive system is very unique, because the juvenile stage is parasitic on fish. Larva called glochidium attach themselves to the gills and the fins of a fish host. The fish's tissue reacts by growing around the glochidia. After several weeks, the parasitic larval form is released and develops into free-living clams.

Mussels use gills like fish to breathe underwater. The water taken in through the siphons for food passes through their gills to deliver the oxygen mussels need to survive. The gills are thin plate-like structures that remove the oxygen that is dissolved in the water. A mussel can be identified by its outer shell. Mussel shells within the same species closely resemble one another. Thus, by examining the mussel's shell, you can identify what type of mussel it is.