[2] The Dümmersee: Diummeri … westphalian for dumb, moist, damp (regarding land), norwegian dumma, unclear air, misty corner.

One and a half miles to the west, the Damme Hills begin to rise, eventually reaching a height of 145 m. Around the lake are fens (Niedermoore) and raised bogs (Hochmoore).

The lake lies in the Dümmer Nature Park, which is just under 500 km2 in area, and in which the Damme Hills and Stemweder Berg form the central elements of the landscape.

To the southwest by the mouth of the River Hunte a tip of the territory of the district of Osnabrück advances to within half a kilometre of the lake.

Previously these headstreams combined with regular heavy rainfall to cause flooding, so that in the 1940s work began to build dykes around the lake.

[5] The reclamation and subsequent lack of annual flooding resulted in algae growing in large quantities in the lake and hence depriving most other organisms of oxygen.