Uels Deth Joeu Falls, Vall d’Aran, Lleida, Spain. 2012.
A thesis about the origin of the Garonne holds that the river rises on the slopes of Pic Aneto, at 2,300 m a.s.l. and flows by way of a sink hole known as the Forau de Aigualluts (42º40′00″N 0º40′01″E) through the limestone of the Tuca Blanca de Pomero and a resurgence in the Val dera Artiga above the Aran Valley in the Spanish Pyrenees. This underground route was suggested by the geologist Ramond de Carbonnieres in 1787, but there was no confirmation until 1931, when caver Norbert Casteret poured fluorescein dye into the flow and noted its emergence a few hours later 4 kilometres (2.5 mi) away at Uelhs deth Joeu (“Jove’s eyes” 42º40′51″N 0º42′28″E) in the Artiga de Lin on the other side of the mountain. From Aigualluts to the confluence with the main river at the bed of the upper Garonne valley (800 m a.s.l.), the Joeu has run for 12.4 km (16 more to get to the French border), carrying 2.16 m3/s. of water, while the main river is carrying 17.7 m3/s.