The Edersee, also known as the Ederstausee, is an 11.8 km (4.6 sq mi) reservoir in Waldeck-Frankenberg, Hesse, Germany holding back an estimated 199.3 million m (7.04 billion cu ft). It has the second-largest area (behind the Forggensee), and the third-largest volume (behind the Bleilochstausee and Rurstausee), of all reservoirs in Germany. It is on the chief western tributary of the Fulda, the Eder, behind the 48 m-high (157 ft) Edersee Dam near the town of Waldeck in the Waldeck-Frankenberg district of North Hesse.

The dam and reservoir are owned by the Federal Waterways and Shipping Administration, whose Hann. Münden Waterways and Shipping office is locally responsible. The primary purpose is provision of water for the federal waterways, the Oberweser and Mittellandkanal. The dam also protects downstream residents from small and medium floods, generates electrical energy and the lake is used for sports and leisure.

Being in the Naturpark Kellerwald-Edersee and the Nationalpark Kellerwald-Edersee and overlooked by Waldeck Castle, it and its surroundings constitute a large recreational/touristic area, economically as well as a reserve for mature trees, woodland flowers, fungi and lichens, wildflowers, animals such as deer, foxes, badgers and occasionally the Eurasian wolf.

This fairly brief central portion of the Eder has its dam near Hemfurth-Edersee, about 35 km (22 mi) south-west of Kassel, linked by a winding road. The lake stretches from the joining of a tributary, short of Herzhausen, in the west to the dam aforesaid. Beyond an intermittent band of tree-lined fields to the south associated with two shoreside villages is the "Ederhöhen", very high, often steep, wooded foothills to the Kellerwald mountain range – together they form a protected upland forest roughly congruent with the Nationalpark Kellerwald-Edersee.

This is the largest lake in Hesse. It takes in four bends, sharp meanders, to its south side.

• Edersee Dam