Garonne, an important river of SW. France, which rises in the Val d'Aran in the Spanish Pyrenees; 26 m. from its source it enters France near Pont du Roi, and after it passes Toulouse flows in a north-westerly direction; joined by the Dordogne, 20 m. below Toulouse, it gradually widens into the Gironde estuary, which opens on the Bay of Biscay; it has a length of 346 m., and is freely navigable as far as Toulouse.