Like most of the great caves, Gouffre Géant de Cabrespine was carved out by waters through the limestone massif.

The river of La Clamoux disappears just before the exit of the village of Cabrespine, and nearly during 10 months per year, downstream, it only becomes a pebble river since the water flows into the Gouffre, to the great displeasure of the inhabitants of the villages located downstream who had deplored this capture of water since the Middle Ages.Popular legends had it that waters used to flow out above Lastours, at the resurgence of Le Prestil. A proof of this is the fact that ducks crossing the underground river had disappeared near Gaougnas would have appeared again in the water currents close to the Cathar Castles of Lastours.

Sure and indisputable is the colouring of waters with fluorescein carried out by speleologists. To date, the underground river has been traced and partially explored on a distance of 17 kilometres approximately. Attempts were even made to dive under wetted roofs but nobody could follow completely the “duck way”.

The underground river situated at the bottom of the Gouffre is already 36m lower than the water capture. Its important flow is between 320m³ and 350m³ above the lowest water level. It certainly increases, however in small proportions, when La Clamoux is in flood.