Seems to me this needs a section on canal waterway tunnels as opposed to water supply tunnels e g Rove Tunnel southern section of the Marseilles Rh ne Canal 4 5 mi 7 2 km long and 72 ft 22 m wide Bouches du Rh ne dept SE France opened 1927 Starting near the village of Le Rove it cuts through the Cha ne de l Estaque at sea level It is considered one of the greatest pieces of engineering since the Panama Canal Longest canal tunnel in the world