The Aff is a river in Brittany, western France. It is a 65-kilometre (40 mi) long tributary of the river Oust. It is canalized for 7 kilometres (4.3 mi) between Glenac (its confluence with the Oust) and La Gacilly.
Coordinates: 47°43′1″N 2°7′38″W / 47.71694°N 2.12722°W