The Senio is a river of Romagna in Italy, the final right-sided tributary of the river Reno. The source of the river is in the province of Florence in the Appennino Tosco-Emiliano mountains. The river flows northeast into the province of Ravenna and flows near Casola Valsenio, Riolo Terme, Castel Bolognese, Cotignola, Lugo, Bagnacavallo, Fusignano and Alfonsine before entering the Reno. The river has a tributary called the Sintria that flows into it east of Riolo Terme.
The mean discharge at its mouth is about ; however this can vary from a minimum of to a maximum of .