Open-water diving

Open-water diving has at least two meanings in underwater diving:

1. In diver training, divers progress from learning diving skills in "confined water" (usually swimming pools) to practicing skills in "open water", which normally implies the sea or a lake, including flooded quarries, in which the environment is not restricted to a small, controlled locality and depth, with conditions typical of a natural body of water which might be used by divers. and the range of hazards and associated risk is significantly expanded. In this context confined water is a special case of open water, as it complies with the more general condition of unobstructed access to the surface.
2. Diving in an environment where the diver has direct vertical access to the surface of the water 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. Penetration diving—involving entering caves or wrecks, or diving under ice—is therefore not "open water diving". In some contexts the lack of a decompression obligation is considered a necessary condition for classification of a dive as an open water dive, but this does not affect the classification of the venue as open water.

Some recreational diver certification agencies use a variation on this term in the title of their entry level certification. Open Water Diver certification implies that the diver is competent to dive in open water of the first meaning, with various constraints regarding the conditions, and particularly that their competence is limited to diving in open water of the second meaning.