Freshwater mussels are bivalve mollusks dating back to the Triassic Period more than 250 million years ago, but they are in trouble: over 70% of mussel species are endangered and 37 are already extinct, making them the most endangered group of organisms in the United States, and they are listed as an endangered species in Ohio. Opened in 2002, the Columbus Zoo Mussel Facility is one of 15 centers in North America capable of growing mussels. It is located on a 32-acre peninsula on the O'Shaughnessy Reservoir of the Scioto River, where water from the river is used for all the aquatic needs of the facility. The facility houses 39 species of mussels, as well as hundreds of Ohio native fish and snails. Eastern hellbenders are North America's largest amphibian, growing more than 2.5 feet long and weighing over 2 lbs., and are completely harmless to humans despite nicknames such as snot-otter, devil dog, and mud-devil. They are listed as an endangered species in Ohio. The Columbus Zoo and Aquarium works closely with the Ohio Department of Wildlife and other environmental organizations to restore hellbender populations; its recovery action program includes collecting and hatching eggs, rearing babies until about three years of age, and releasing them back to the wild. Since 2012, over 900 hellbenders have been introduced to healthy Ohio streams and rivers.