Any time you’re diving at 300 to 3000 metres/1000 to 10,000 feet above sea level, you're altitude diving. At altitude, atmospheric pressure is lower than at sea level, so surfacing at the end of an altitude dive leads to a greater reduction in pressure and an increased risk of decompression sickness. The dives are also typically carried out in freshwater at altitude so it has a lower density than seawater used for calculation of decompression tables. The amount of time the diver has spent at altitude is also of concern as divers with gas loadings near those of sea level may also be at an increased risk. The US Navy recommends waiting 12 hours following arrival at altitude before performing the first dive. For an altitude dive in Switzerland we can recommend a dive in the Caumasee a picturesque lake nestled in the woods close to Flims in the canton of Graubünden. Created by a prehistoric rock slide, it can only be reached by a footpath or by a funicular railway built in 1939. The particularity of the lake is that it is fed from underground sources rather than being fed by river or rain fall. It is located 997m asl and has a maximum depth of 30m.
Altitude diving is the territory for extreme divers and the Alpina professional diving watch collection.