Leopoldsteinersee, Mountain lake in Eisenerz, Austria.

Leopoldsteinersee is a mountain lake in the Hochschwab range, distinguished by its emerald-green water and surrounded by forested slopes. The lake stretches approximately 1,400 meters long, around 370 meters wide, and reaches depths up to 31 meters.

The lake takes its name from nearby Leopoldstein Castle. On 7 April 1945, members of the Eisenerz Volkssturm carried out the largest massacre in Styria near the Präbichl pass, killing over 200 Jews; their bodies were transported by truck to the Seeau by Leopoldsteinersee and buried in mass graves. In 2023 the artist Ramesch Daha, working with the municipality of Eisenerz, created a two-part memorial based on extensive research into these events.

The lake's name comes from nearby Leopoldstein Castle. A local legend tells that a water sprite was caught near the shore; to buy his freedom he showed his captors the iron deposits at the Erzberg, a few kilometres away, then vanished into a water hole. The Seebach flows through the lake, which is fed mainly by underground springs.

A 3-kilometre trail circles the lake, and the North Alpine long-distance route (part of European trail E4) briefly touches the shore on its way from the Hochschwab to Eisenerz. A local operator rents electric and rowing boats. On 7 October 2023 the lake hosted the 23rd brass and echo players' meeting, organised by the Eisenerz town band.

A local legend tells that a water sprite was caught near the lake; to buy his freedom he showed his captors the iron deposits of the Erzberg, only a few kilometres away, then vanished into a water hole. The lake is named after nearby Leopoldstein Castle.