The Eder is a 177 km long river in Germany, and a tributary of the Fulda River. It was first mentioned by the Roman historian Tacitus as the Adrana in the territory of the Chatti.
The river rises from the Ederkopf mountain in western North Rhine-Westphalia near the springs of the Lahn and Sieg rivers. Unlike the Lahn and Sieg, that are both tributaries of the Rhine, the Eder flows east and north and into the river Fulda at Edermünde, south of Kassel. At Hannoversch Münden, the Fulda joins with the Werra to form the Weser river which flows into the North Sea north of Bremen. Towns along the course of the Eder include Battenberg, Frankenberg, Waldeck and Fritzlar.
A rock-and-concrete dam (47 m high, 400 m long) completed in 1914 near the small town of Waldeck created the large Edersee reservoir, which is 27 km long and has a holding capacity of 200 million m³ of water. It is used to generate hydro-electricity and to regulate water levels for shipping on the Weser river.
The dam was destroyed by British Avro Lancaster bombers of the RAF's 617 Squadron on 17 May 1943 (Operation Chastise). The bombers were equipped with special Barnes Wallis bouncing bombs. On the same night, the nearby Möhne Reservoir dam was also attacked, causing enormous destruction and loss of life downstream (the great majority of drowning victims were Ukrainian POWs in a labor camp just below the dam). The story of the raid was made into a film called The Dam Busters.
The dam was rebuilt the same year, and the lake today is a major summertime recreation facility, particularly popular with Dutch campers and tourists. Eder was included as a multiplayer map in the 2006 video game Call of Duty 3