150º Panorama of the Aran Valley from the Beret Plateau, showing the Ruda-Garona and Beret-Garona confluence. In Vielha
the Garonne turns westward (out of sight), and after 12 kilometres (7 mi) receives water from the Joèu (Pic Aneto).
The Main Lake of Saboredo and Pic de Saboredo, the head of the Garonne valley.
The water from Barrancs and Escaleta ravines disappears into the ground at Forau de Aigualluts
The Garonne's headwaters are to be found in the Aran Valley in the Spanish Pyrenees, though three different locations have been proposed as the true source: the Uelh deth Garona at Plan de Beret (42°42′34″N 0°56′43″E / 42.709494°N 0.945398°E), the Ratera-Saboredo cirque 42°36′26″N 0°57′56″E / 42°36′26″N 0°57′56″E / 42.607295; 0.965424), or the slopes of Pic Aneto (Salterillo-Barrancs ravine 42°38′59″N 0°40′06″E / 42°38′59″N 0°40′06″E / 42.6498; 0.6683 according to the season).
The Uelh deth Garona at 1,862 metres (6,109 ft) above sea level has been traditionally considered as the source of the Garonne. From this point a brook (called the Beret-Garona) runs for 2.5 kilometres (1.6 mi) until the bed of the main upper Garonne valley. The river runs for another 38 kilometres (24 mi) until the French border at Pont de Rei, 40.5 kilometres (25.2 mi) in total.
The Ratera-Saboredo cirque is the head of the upper Garonne valley, and its upper lake at 2,600 metres (8,500 ft) above sea level is the origin of the Ruda-Garona river, running for 16 kilometres (9.9 mi) until the confluence with the Beret-Garona brook, and another 38 kilometres (24 mi) until the French border at Pont del Rei, 54 kilometres (34 mi) in total. At the confluence, the Ruda-Garona carries 2.6 cubic metres per second (92 cu ft/s) of water. The Ratera-Saboredo cirque has been pointed by many researchers as the origin of the Garonne.
The third thesis holds that the river rises on the slopes of Pic Aneto at 2,300 metres (7,500 ft) above sea level and flows by way of a sinkhole known as the Forau de Aigualluts (42°40′00″N 0°40′01″E / 42°40′00″N 0°40′01″E / 42.6666; 0.6669) through the limestone of the Tuca Blanca de Pomèro 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 Carbonnières 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 Joèu ("Jove's eyes" 42°40′51″N 0°42′28″E / 42°40′51″N 0°42′28″E / 42.68092; 0.7077) 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 at 800 metres (2,600 ft) above sea level, the Joèu has run for 12.4 kilometres (7.7 mi) (16 kilometres more to get to the French border), carrying 2.16 cubic metres per second (76 cu ft/s) of water, while the main river is carrying 17.7 cubic metres per second (630 cu ft/s).
Despite the lack of universal agreement upon definition for determining a stream's source, the United States Geological Survey, the National Geographic Society, and the Smithsonian Institution agree that a stream's source should be considered as the most distant point (along watercourses from the river mouth) in the drainage basin from which water runs.
The Ratera-Saboredo cirque is the "most distant point (along watercourses from the river mouth) in the drainage basin from which water runs", and the source of the Garonne, according to the United States Geological Survey, the National Geographic Society, and the Smithsonian Institution convention upon determining a stream's source.
The Garonne follows the Aran Valley northwards into France, flowing via Toulouse and Agen towards Bordeaux, where it meets the Gironde estuary. The Gironde flows into the Atlantic Ocean (Bay of Biscay). Along its course, the Garonne is joined by three other major rivers: the Ariège, the Tarn, and the Lot. Just after Bordeaux, the Garonne meets the Dordogne at the Bec d'Ambès, forming the Gironde estuary, which after approximately 100 kilometres (62 mi) empties into the Atlantic Ocean. Other tributaries include the Save and the Gers.
The Garonne is one of the few rivers in the world that exhibit a tidal bore. Surfers and jet skiers could ride the tidal bore at least as far as the village of Cambes, 120 kilometres or 75 miles from the Atlantic, and even further upstream to Cadillac, although the tidal bore appears and disappears in response to changes in the channel bathymetry. In 2010 and 2012, some detailed field studies were conducted in the Garonne's Arcins channel between
Arcins Island and the right bank close to Lastrene township. A striking feature of the field data sets was the large and rapid fluctuations in turbulent velocities and turbulent stresses during the tidal bore and flood flow.
European sea sturgeon conservation
The European sea sturgeon (Acipenser sturio), also known as the Atlantic sturgeon or common sturgeon, is now a Critically Endangered species (IUCN) status. This species of sturgeon that can reach a length of 6 m (20 ft) and weigh 400 kg (880 lb) and can reach an age of 100 year  Previously found on most coasts of Europe, it has now become so rare that they ONLY breed in the Garonne river basin in France. Conservation projects are under way to save this fish from extinction with species reintroduction from aquaculture with the first releases being made in 1995.
Towns along the river