An alligator is a crocodilian in the genus Alligator of the family Alligatoridae. The two living species are the American alligator (A. mississippiensis) and the Chinese alligator (A. sinensis). American alligators live in freshwater environments, such as ponds, marshes, wetlands, rivers, lakes, and swamps, as well as in brackish environments. When they construct alligator holes in the wetlands, they increase plant diversity and provide habitat for other animals during droughts. The Chinese alligator currently is found only in the Yangtze River valley and is extremely endangered, with only a few dozen believed to be left in the wild. Indeed, far more Chinese alligators live in zoos around the world than can be found in the wild.