The Senio is a 92 km river of Romagna in Italy, the final right-sided tributary of the river Reno. The mean discharge at its mouth is about 10 m³/s; however this can vary from a minimum of 0.3 m³/s to a maximum of 500 m³/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.