Open Water Diver is an entry-level full diver certification for scuba diving. Experienced divers progress from diving in swimming pools to "open water", which means either the sea or a lake, or any diving where the surface of the water is in contact with the Earth's atmosphere. "Open water diving" implies that if a problem arises, the diver can directly ascend vertically to the atmosphere to breathe air. Maximum diving depth for that qualification is 18m.