A maar volcano created this broad basin which is about 1.5 kilometres in diameter.
There was originally a maar lake in the basin, but this became silted up. Already in Roman times, however, a dam was built to create a pond stocked with lots of fish. After the pond was drained in 1838, the western part was used as arable land.
It is now meadowland where we stand today, while the eastern part has been taken over by bogland. Turf was dug there until the 1950s. The fenland with eared willow and buckthorn shrubs is now protected as a nature reserve.