A public aquarium (plural: public aquaria or public aquariums) is the aquatic counterpart of a zoo, housing aquatic species for viewing. Most public aquaria feature a number of smaller tanks, as well as those greater in size than could be kept by most any home aquarist. Since the first public aquriums built in in the mid-1800s they have become very popular and their numbers have dramatically increased. Most modern aquaria focus on conservation issues and educating the public.
Modern day aquarium tanks can hold millions of U.S. gallons of water and can house large species, including dolphins, sharks or beluga whales. This is accomplished though thick, clear acrylic glass windows. Aquatic and semiaquatic mammals, including otters, and seals are often cared for at aquaria. Some establishments, such as the Oregon Coast Aquarium, have aquatic aviaries.