The Bienne rises at the confluence of the Bief de la Chaille and the Biennette upstream of the Morez Cluse, at the foot of Mont Fier. Flanked to the east and west by very steep slopes, it cuts deeply into the folded Jura massif as far as Saint Claude. Its slopes, most of which are forested, become inaccessible in places, with steep cliffs, particularly around the small village of Lézat.