Ла-Фер
The Serre () is a tributary of the river Oise in northern France, in the departments of Ardennes and Aisne. Its source is in the small village of La Férée, Ardennes, from which it flows west into the Aisne department. It flows through Montcornet, Marle and Crécy-sur-Serre and joins the Oise at La Fère. Its total length is .