Dolphins are found in almost all the seas and oceans of the world. Although some species are restricted to small areas, many, such as the common dolphin, or bottlenose dolphin, are found worldwide. Several species are found in fresh water, notably the Ganges River dolphin. The rivers of South America are home to the long-snouted dolphin and the small, graceful Sotalia fluviatilis. The latter is known to live as far as fifteen hundred miles up the Amazon River. Dolphins are plentiful in certain areas of the world. Off the coast of Japan, the population of the white-sided dolphin is estimated at between thirty and fifty thousand. In many species, schools of up to a thousand dolphins travel together. Some species, such as the bottlenose dolphin, are usually found in small groups of less than a hundred, or in even smaller family groups. Solitary dolphins are rare.