In 2003, Germany began flooding a former coal pit; by 2011, it had become a 1,840-hectare lake home to 240 bird species

Somewhere in Germany there’s a huge hole left behind by decades of coal mining. Eventually that same hole became a clear lake with divers below and birds above. That’s Geiseltalsee in Saxony-Anhalt. The Global Nature Fund says the lake was mined for lignite in the past and was transformed into a thriving habitat in the roughly three decades since mining ended. The group named it the Living Lake of the Year on World Water Day 2023. That was the first man-made lake to win that title.

A once-mined pit, now hosts diverse aquatic life. (AI-generated/ChatGPT)From coal pit to giant lakeFor generations, crews dug lignite, a soft brown coal, from the Geiseltal valley. Coal mining there stopped in 1993. What was left, the Global Nature Fund describes, was a hostile pit for life in a bare mining landscape.

And then a new plan was proposed. By 2003, workers began preparing the remaining pit for flooding, a job that took eight years to complete. When the work was finished in 2011, the lake covered 1,840 hectares, or about 4,500 acres. The group says the lake is up to 76 meters deep and holds 423 million cubic meters of water. That's 423 billion liters, about 170,000 Olympic swimming pools. As of 2023, the group called it Germany's largest artificial lake.

The valley was well known before the lake was created. Coal mines there also yielded fossils of plants and animals from about 45 million years ago, during a period called the Eocene. Most of the old pits are now flooded. Yet, fossils exist in collections that scientists continue to study.

Daniel Falk and colleagues show this in a 2024 study in Scientific Reports. The team looked at 168 fossil frog and toad specimens from the Geiseltal collection at Martin Luther University Halle-Wittenberg. They discovered that the soft tissue had survived in two distinct layers. The study also did not support the earlier claim that silica had duplicated the tissue. So the lake lies in a valley already significant to science.

Geiseltalsee is nutrient-poor, and its water is very clear. The Global Nature Fund says the clarity allows stoneworts, a type of algae, to grow down to about 13 meters. The lake also supports aquatic insects, fish and 240 bird species, 108 of which breed around its shores. Protected birds that have found a new home there include common terns and bee-eaters.

The shore is a mix of reed beds, grassland, shrubs and steep cliffs. The variety gives plants and birds many places to live. Local conservationists care for cliffs where the bee-eaters and sand martins nest. As of 2023, local dive groups had trained 25 conservation divers, who check the lake's underwater plants each year.

In 2023, the Global Nature Fund called the lake's ecological condition very good, but warned that use was growing. Boating, fishing and disturbance were already reaching protected resting and breeding areas.

On May 20, 2026, the Saalekreis district changed its rules for the lake, opening the northern part of the lake and a kitesurfing area on the south shore. It was challenged by the conservation group NABU. On August 21, 2026, the Halle administrative court ruled in favor of NABU in an emergency procedure. The northern part remains closed to leisure use for now, though the district can appeal to the state's higher administrative court.

Geiseltalsee might not be a perfect story, but it’s a hopeful one. Clear water and protected birds are now found in a former mining pit. Dr. Thomas Schäfer, who leads nature conservation at the Global Nature Fund, called it a largely successful restoration in 2023. The task now, he said, is securing the future of the young ecosystem. It might be easy to say but hard to do: to share the lake and not wear it away.

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