The Santerno River (total length: 99 km) has its source in the Futa Pass and flows along its valley for 68 km. The tract flowing through hills and mountains is considered as one of the most interesting of the Emilian-Tuscan Appennine. The river has lush and steep banks and sandstone cliffs. Its clean waters are home of a variety of fish. A wide range of geological formations can be observed: Pleistocene clays (dating back to 2-5 million years ago), chalks, sands and marble-like formations.
For all these reasons, Santerno river is one of Castel del Rio's most important tourist resources. Areas equipped for swimming, picnics and fishing are scattered all along the river's course up to the border with Tuscany. Lido di Valsalva is a good example of it. A beautiful "No-kill" area offering hauls of barbel and chub is located downstream from Castel del Rio.
In spring, a 25 km tract of the Santerno becomes a focal point for canoeing enthusiasts. The quality of its waters and its flow are perfect for this sport especially from April to May. While alpine rivers froze in winter, the Santerno is often practicable from October to January. In the remaining months, the river offers small stretches of water for school activities.