The Saine is a French river that flows through the Jura department in the Bourgogne-Franche-Comté region.

Nineteen kilometers long,[1][2] the Saine rises in a green, sparsely populated area, in the small village of Foncine-le-Haut, in the Haut-Jura Regional Nature Park, at an altitude of around 892 m.[3] First, it heads south-west, then, on reaching Foncine-le-Bas, it bends north-west and cuts deeply into the limestone plateau, creating the gorges de Malvaux, where it receives a right-bank tributary, the Bief de la Ruine, with its famous waterfall.

Near the village of Les Planches-en-Montagne, it creates a spectacular 1 km-long fault, the Gorges de la Langouette.

[1] The water level flowing through the basin is 1,360 millimeters per year, which is very high, four times higher than the average for France as a whole, and also higher than the average for the Ain basin, which is already very high (1,070 millimeters per year at Chazey-sur-Ain).

[8] Covering more than 1,100 hectares, the upper Saine valley has been classified under the French Environment Code since September 2011 for its picturesque character.