The Möhne Reservoir is an artificial lake in Northrhein-Westphalia, some 45 km east of Dortmund. The dam was built in 1908-1913 to help control floods, regulate water levels on the Ruhr river downstream, and generate hydropower. Today, the lake is also a tourist attraction. The lake is formed by the damming of two rivers, Möhne and Heve, and with its four basins stores as much as 135 million cubic meters of water. Westphalia (in German, Westfalen) is a (historic) region in Germany, centred on the cities of Dortmund, Münster, Bielefeld, and Osnabrück and now included in the Bundesland of North Rhine-Westphalia (and the (south-)west of Lower Saxony). ... Map of Germany showing Dortmund Dortmund is a city in Germany, located in the Bundesland of North Rhine-Westphalia, in the Ruhr area. ... The Ruhr in Essen-Kettwig The Ruhr is a large river in western Germany (North Rhine-Westphalia) starting near the town of Winterberg in Sauerland and ending in the Rhine in the city of Duisburg. ...

The dam was destroyed by British bombers ("The Dambusters") during the night of 16-17 May, 1943, together with the Edersee dam in northern Hesse (see Operation Chastise). Special bouncing bombs had been constructed which were able to roll over the protective nets that hung in the water. A huge hole of 77 m by 22 m was blown into the dam. The resulting huge floodwave spilling from the lake killed between 1,200 and 1,600 people. The effect on the German war effort was minimial, as the dam was fully repaired again by October 1943. The Eder barrier, which creates the Edersee. ... With an area of 21,110 km² and just over six million inhabitants, Hesse (German Hessen) is one of Germanys sixteen federal states (Bundesländer). ... Operation Chastise was the official name for the attacks on German dams on May 17, 1943 in World War II using a specially developed bouncing bomb. The attack was carried out by Royal Air Force No. ...