Meager poplulations may be the result of water degradation. Mussels are extremely sensitive to environmental change. A mollusk that was introduced into the waters of the Congaree River is the Asiatic clam. This clam has become a nuisance, overpopulating many areas and adversely impacting native species. Other mollusks found in the Congaree Swamp are snails and slugs.
Visitors often see numerous holes in the trails and sloughs.
These are the homes of the numerous crayfish which thrive in the wetland environment. The crayfish are prime food for barred owls and raccoons. Owl pellets, containing pieces of crayfish shells, can be found on the boardwalk railings. The following is a list of species which potentially can be found at the Congaree Swamp National Monument. Many of these species have been documented onsite, however the list also includes species which have NOT been documented.