In the later stages of initial Diver Training , divers progress from diving in swimming pools to "open water", where "open water" normally means the Sea or a Lake .
Any diving where the surface of the water immediately above the diver 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 . So, Penetration Diving involving entering caves or wrecks or diving under ice is not "open water"" diving.
