organized exploration of the basin and on 24 September 1938 Negri reached a depth of . It was then necessary to wait for the arrival of the scuba diving suit in 1946 when Jacques Cousteau reached , then nine years later. This is the limit of dives with air. In 1981 Claude Touloumdjian reached with an oxygen-helium mixture. Finally, in 1983, Jochen Hasenmayer reached . To go even deeper and touch the bottom it would be necessary to use robots. In 1985 the Modexa 350 Mission removed the mystery about the depth of the system. The robot touched bottom at a depth of . In 1989 another robot, Spélénaute (SSFV), reached the lowest point known to date in the siphon at a depth of . In 1997 the diver Pascal Bernabé descended to a depth of . In 2014 a virtual tour was created by the photographer Christoph Gerigk in collaboration with the Speleological Society of Fontaine de Vaucluse (SSFV) from 360° spherical panoramic views. Today, the joint efforts of geologists, hydrogeologists, hydrochemists and speleologists have made it possible to gain a better understanding of the functioning of this karst spring. Its catchment receives waters from Mont Ventoux, the Vaucluse Mountains, the Albion Plateau and Lure Mountain, but it excludes Bluye Mountain in the north, as well as the Luberon massif and the Apt syncline in the south. The part of the reservoir that is accessible to speleologists exceeds a depth of , since it has been explored during a period of low water from several open cavities forming the karst system of the Souffleur hole of Saint-Christol, the "underground river of Albion". This system of chasms and cavities, which riddles the Albion Plateau, is one of the effects of karstification. During heavy storms, it can store around . A mathematical model indicated that, based on the greatest depth of and the surface area of the catchment, permanent reserves could reach . Over the course of a decade, the annual flow varies between . With an average of per second, it yields seven times more than all the drinking water distributed in the department of Vaucluse. It is the largest spring in France by volume of water released, and ranks fifth among the world's largest springs. Notes Sources Karst springs Geography of Provence-Alpes-Côte d'Azur Geography of Vaucluse