There is extensive water travel, both along the thousands of rivers and lakes and along the immense coastline. The Ohio River alone, for instance, conveys a greater volume of traffic than any other single inland channel in the world. Most U.S. cities that front the water have passenger and auto ferries. Passenger and freight lines and tour ships traverse all of the Great Lakes, with ports in Duluth, Sault Sainte Marie, Milwaukee, Chicago, Detroit, Buffalo, Rochester, Cleveland, and Toronto. International cruise ships call at all major ports.