 During World War II, two of the dams on the Ruhr, the Möhne Dam and the Sorpe Dam were targets for Operation Chastise, in which special "bouncing bombs" were developed to take out the dams and flood the valley, with the hope of seriously affecting the German industries there.The story was told in a 1951 book and the popular 1955 film made from it, "The Dam Busters".There are five Ruhr reservoirs on the river, often used for leisure activities.