Hainer See, Artificial lake in Landkreis Leipzig, Germany.

Hainer See is a large artificial lake in Landkreis Leipzig with a water surface of around 565 hectares and a shoreline stretching approximately 15 kilometers. The lake reaches depths of up to 49 meters in places, creating varied conditions across its basin.

The lake developed from a former brown coal mining site that operated between 1942 and 1993, then gradually filled with water. The transformation from industrial pit to recreational lake took place between 1999 and 2010, creating a new landscape from old mining grounds.

The lake is named after the village of Hain, which was demolished for the Witznitz II open-cast mine and whose former land now lies under the water. A memorial stone placed at the shore in 2005 during the Hain-Kreudnitz meeting commemorates Hain and the nearby village of Kreudnitz, also lost to the mine. The lake has been developed for tourism since 2008.

The lake is reached via a canal to the Pleiße, finished in 2010, and the water is kept at recreation quality by adding dissolved burnt lime during flooding. A campsite opened on the north shore between Rötha and Espenhain in 2015; the Lagune Kahnsdorf area, on the former Kahnsdorf works site, is being developed with building plots.

The lake sits where industrial scars once marked the landscape, showing how nature can reclaim a mining site over time. Visitors can witness the transformation of a barren extraction zone into a place where sailors, birdwatchers, and swimmers now gather.