6.5 km long circular trail is around the Kinzig reservoir in Hesse.
Incidentally, this lake serves as flood protection for the region around Hanau and for energy generation. You will also find great toilets on the tour.
Source: https://www.seen.de/kinzig-stausee/
Photo: https://de.wikipedia.org/wiki/Kinzigtalsperre#/media/Datei:Kinzigtalsperre_komplett.jpg