SF Hydro was a Norwegian steam powered railway ferry that operated on Tinnsjø in Telemark. The ferry operated between Mæl and Tinnoset between 1914 and 1944, connecting the two railways Rjukanbanen and Tinnosbanen. The railway was used to transport raw materials and fertilizer from Norsk Hydro's factory at Rjukan to the port in Skien. She was the target of a Norwegian operation on 20 February 1944, when resistance fighters sank the ferry in the deepest spot of Tinnsjø in order to prevent Nazi Germany from sending heavy water to Germany.