The river warbler (Locustella fluviatilis) is an Old World warbler in the grass warbler genus Locustella. It breeds in east and central Europe into western Asia. It is migratory, wintering in east Africa. The genus name Locustella is from Latin and is a diminutive of locusta, "grasshopper". This refers to the song of the common grasshopper warbler and some others in this genus. The specific fluviatilis is Latin for "of a river".