Hennetalsperre, Reservoir in Meschede, Germany

The Hennetalsperre is a reservoir created by a 60-metre-high rockfill dam with an asphalt concrete surface seal, completed in 1955 about 200 metres upstream of the earlier dam. The dam is 376 metres long and holds back 38.4 million cubic metres of water, making it an over-year storage basin. The reservoir lies almost entirely in Meschede's Berghausen and Mielinghausen districts, with only the main dam area in Meschede proper.

The first dam on the Henne was built between 1901 and 1905 by the Talsperrengenossenschaft der Oberen Ruhr, with annual support of 110,000 marks from the Ruhrtalsperrenverein founded in 1899. Its 38-metre masonry wall impounded 11 million cubic metres, but carbonic acid dissolved the limestone bedrock, creating up to 20-metre-wide and over 100-metre-deep cavities; the dam became leaky and was emptied on 20 December 1948. About 200 metres upstream, a new 60-metre rockfill dam with asphalt concrete sealing entered service in 1955, holding 38.4 million cubic metres.

The lake hosts regular rowing competitions, and anglers buy day permits to fish its waters. A signposted cycling route, the HenneseeSchleife, runs along the shore, and a large holiday cottage park sits at the southern end. Swimming is allowed only at a few designated spots.

The reservoir lies a few kilometres south of Meschede, with the main dam in the Meschede district and the water stretching into Berghausen and Mielinghausen. Swimming is permitted only at a few marked spots. A signposted cycle route, the HenneseeSchleife, runs along the lake, and anglers need a day ticket.

In very hot summers such as 1976 and 2018, when the water level drops extremely low, the old bridge of the village of Hellern and parts of the former B 55 road become visible on the reservoir bed. The villages of Hellern, Mielinghausen, Enkhausen and Immenhausen were flooded when the new dam was built.