The Allier (Occitan: Alèir) is a river in central France, left tributary to the river Loire. Its source is in the Massif Central, in the Lozère département, east of Mende. It flows generally north. It joins the river Loire west of the city Nevers.
The Allier River is one of the rare places in Southern Europe where the freshwater grayling (Thymallus thymallus), known in French as ombre des rivières, occurs in a natural habitat.
Grayling like to live in shoals and are sensitive to pollution. In the Allier River these fish are more abundant in the stretch of the river between Langogne and Brioude. They are economically important, being appreciated for food and fished for sport.