The Blanche (French pronunciation: [blɑ̃ʃ] ⓘ) is a tributary of the left bank of the Acheneau and thus a sub-tributary of the Loire.

[2] 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.

It has its source in the east of Chaumes-en-Retz and it flows eastward, fed from the north by streams from the Forêt de Princé [fr] 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.