A group of organisms that primarily live and thrive in water environments, including oceans, seas, lakes, ponds, rivers, and streams. They encompass a variety of species ranging from fish, crustaceans, mollusks to larger marine mammals such as whales and seals. These animals are specially adapted to their aquatic habitats, with features that enable them to swim, dive, or float. They play significant roles in the ecosystem, contributing to the balance of aquatic life, food chains, and biodiversity.