The Senio is a 92-kilometre (57 mi) river of Romagna in Italy, the final right-sided tributary of the river Reno. The mean discharge at its mouth is about 10 cubic metres per second (350 cu ft/s); however this can vary from a minimum of 0.3 cubic metres per second (11 cu ft/s) to a maximum of 500 cubic metres per second (18,000 cu ft/s).
It was the site of a major engagement in 1945 during World War II. The Allied capture of the Senio River area was critical for the success of the Allied drive to capture all of Italy. The British 8th Army took great casualties in crossing the heavily defended river.