Talsperre Lehnmühle, Cultural heritage reservoir in Dippoldiswalde and Hartmannsdorf-Reichenau, Germany.

The Talsperre Lehnmühle is a dam in the Ore Mountains, situated between Dippoldiswalde and Hartmannsdorf-Reichenau, where it holds back a large reservoir surrounded by forests. The water stored here serves both as drinking water supply and as protection against flooding for communities downstream.

Built between 1927 and 1931, the Lehnmühle dam was the third reservoir project in the eastern Ore Mountains after Malter (1908–1913) and Klingenberg (1908–1914), following the severe flood of summer 1897. Its technical equipment came from the Polte-Werke, and the road from Schmiedeberg to Frauenstein, today the B 171, had to be rerouted over a dam crest at the upper end of the reservoir.

The dam takes its name from the Lehnmühle, a watermill first documented in 1536 that ground grain and cut timber; a wood-pulping plant was added around 1870. After 1945 an oxygen works and later agricultural machinery production occupied its buildings, which were demolished in late 2006. A small rest area with an information board now marks the site below the dam.

The reservoir is easy to reach by car, with parking available close to the dam structure. Trails run through the forest around the water and are most comfortable to walk in dry weather.

The dam wall is built of gneiss rubble stone from two nearby quarries, not concrete. It was one of the first straight rubble-stone dams in Europe and remains the only straight gravity dam of rubble stone in the former East German states.