The water reappearing at Uelhs deth Joeu was proven via a 1931 experiment where researchers dyed the water at the sinkhole to trace its path.
The sinkhole acts as a hydrological divide between the Esera River basin and the Garonne River basin.
The surrounding landscape is shaped by glacial erosion from the retreating Aneto glacier.
The trail leading to the sinkhole is part of the GR 11 trans-Pyrenean long-distance path.
The site remains one of the most significant examples of karst topography in the Pyrenees mountain range.
Forau d'Aigualluts is a prominent karst sinkhole located in the Benasque Valley, where the waters of the Aigualluts glacier disappear into the limestone bedrock. The water travels underground for approximately 3.6 kilometers before re-emerging at the Uelhs deth Joeu springs in the Val d'Aran. The site is surrounded by the massifs of Aneto and Maladeta, the highest peaks in the Pyrenees. A marked trail leads visitors through the high-altitude meadows of Plan d'Aigualluts. Geologically, this site serves as a massive subterranean drainage system for the Esera River basin. The water flow reaches its maximum volume during the spring thaw of the glacier. Visitors can observe the waterfall plunging into a deep, steep-walled sinkhole surrounded by alpine terrain.
The raised grassy ridge overlooking the sinkhole provides a direct view into the vortex of the waterfall.
Bring a windbreaker even in summer, as temperatures drop rapidly in the high mountain wind.
Start your hike early to secure parking at the La Besurta trailhead, as space is extremely limited.
Wear sturdy, waterproof hiking boots to navigate the occasionally boggy terrain of the Plan d'Aigualluts.
Do not attempt to enter or climb into the sinkhole area, as the limestone rocks are unstable and slippery.
Access road to La Besurta is restricted to shuttle buses during peak summer months; hiking trail access is snow-dependent and generally open from late spring to early autumn.
Stay on marked trails to protect the sensitive alpine tundra vegetation.
