Although freshwater clams are found on every continent except Antarctica, they are now considered one of the most jeopardized groups of animals in the world. Approximately 270 species belong to the family Unionidae, found in North America. A total of 72 percent of our 270 native mussel species are listed as recently extinct, endangered, threatened, or of special concern due to human impact on aquatic habitat, commercial harvesting, the introduction of carp, water pollution, and the invasion of zebra mussels.