Undersea, also known as underwater or subaquatic, is the realm that lies beneath the surface of water. It includes both marine environments and freshwater environments. The study of undersea environments is called oceanography or limnology, depending on the type of water involved.
Life began in the undersea realm and it is thought that many species still remain undiscovered. The undersea environment is home to a vast array of life, from microscopic plankton to giant squid. Undersea habitats include coral reefs, kelp forests, hydrothermal vents, and shipwrecks.
Humans have long been fascinated by the undersea world and have attempted to explore it since ancient times. Early explorers used diving bells and other primitive devices to venture into the depths. Modern technology has allowed humans to reach previously inaccessible areas of the undersea realm, such as the Mariana Trench, which is deeper than Mount Everest is tall.
Despite our advancements in technology, there is still much we do not know about the undersea world. Scientists are constantly discovering new species and uncovering new mysteries about this fascinating environment.