The Seille is a river originating in the Jura mountains in France. It is a left tributary of the Saône, joining it in the commune of La Truchère, in Saône-et-Loire. It is 100 km long.
The river's headwaters are in the reculée (blind valley) of Baume-les-Messieurs, approximately 10 km east of Lons-le-Saunier. From there it crosses the vineyards of the Jura department, irrigating the communes of Nevy-sur-Seille, Voiteur, and Arlay, before reaching the agricultural plain of Bletterans, then Louhans and the Bresse area in the départment of Saône-et-Loire, finally flowing into the Saône at La Truchère, a few kilometers south of Tournus. Near its mouth, the Seille forms a 3047 hectare network of ponds, dunes, and bogs, providing a habitat for a large number of migratory birds, including endangered species and rare plant species.
The upper part of the Seille is a tranquil trout stream that sometimes overflows its banks in the spring. The lower part, also prone to substantial flooding, is navigable for 39 kilometers from Louhans to La Truchère; there one can find catfish that have inhabited the river since the 1960s and that occasionally become very large. The river is known for, in the 1980s, having the largest catches of catfish in France (record: 2.20 m, 66 kg).