| Image Alt: | A small watercourse flowing between a building to the left and a fenced road to the right, bordered by vegetation and with trees on the skyline. |
| Pushpin Map: | France#France Pays de la Loire |
| Subdivision Type1: | Country |
| Subdivision Name3: | Nantes |
| Source1 Location: | Chaumes-en-Retz |
| Source1 Coordinates: | 47.1179°N -1.9297°W |
| Source1 Elevation: | 11,36 |
| Mouth: | Acheneau |
| Mouth Location: | Cheix-en-Retz |
| Mouth Coordinates: | 47.1791°N -1.8301°W |
| Mouth Elevation: | 0m |
| Progression: | Acheneau→ |
| Tributaries Right: | Ruisseau du Bois Beaulieu |
The Blanche is a tributary of the left bank of the Acheneau and thus a sub-tributary of the Loire.
The name, Blanche, meaning white in French, is thought to derive from the presence of white chalk in the water from the lime kilns around Arthon-en-Retz. Another hypothesis is that the name derives from the white mist over its related marshland.[1]
La Blanche is located entirely in the Pays de Retz, south of the Loire in the department of Loire-Atlantique. It covers the municipalities of Chaumes-en-Retz (Arthon-en-Retz and Chéméré), Saint-Hilaire-de-Chaléons, Cheix-en-Retz and Rouans.
The Blanche basin is bordered by the Acheneau basins to the north, the to the east, the Falleron to the south and the Canal de Haute Perche to the west. It has its source in the east of Chaumes-en-Retz and it flows eastward, fed from the north by streams from the and from the south from around Saint-Hilaire-de-Chaléons. After about 7km the river veers north and continues for 9km, fed by several streams from the west and east including the Ruisseau du Bois de Beaulieu at Pont Beranger. Its confluence with the Acheneau is in the marshes of the Marais de Cheix south of Cheix-en-Retz where it divides into two, the Vielle Blanche joining the Acheneau to Buzon while the Blanche continues to the west more channelled in a network of canals, joining the Acheneau further south-west of the town in the Marais d'Acheneau.