The lake is the product of extensive lignite mining in the area which first shows up in the documentary record in 1698 but which only reached significant extent in the late 19th and early 20th century when the first
open-pit mines in the area were started. After World War II, the area came under the control of the
Soviet Occupation Zone which would soon give rise to the
German Democratic Republic (GDR). Due to a desire for
autarky and a dearth of natural resources other than lignite (and uranium in the Ore Mountains, which however mostly went to the
Soviet nuclear program), lignite mining ramped up sharply in the GDR, converting a country of less than 20 million inhabitants to the world's top producer and user of this commodity. As nearby
Leuna had been
a center of the chemical industry, lignite, besides being used for home heating (usually as
briquettes) and for power generation in lignite fired
steam power plants, also saw extensive use as a feedstock for the chemical industry, including through processes such as
coal liquefaction. While coal is less desirable as a chemical feedstock than petroleum, the ability to save on
hard currency by using it to substitute petroleum made it the preferred solution in East Germany. After German reunification, the demand for lignite dropped sharply as reunified Germany could import petroleum on the world market and superior domestic hard coal from the
Ruhr area and other then-active mining areas in West Germany competed with lignite. Furthermore, lignite is by far the most ecologically damaging fossil fuel due to its high moisture content, high sulfur content (producing
acid rain upon combustion) and frequent contamination with
toxic heavy metals. Thus it was decided to wind down large parts of East German lignite mining with the mines now covered by the lake shut down in 1993. By that point some of lignite and a similar amount of
overburden had been mined over the existence of the mine and some 12,500 people who had lived on land now taken up by mining had had to be resettled. While there had been vague plans to flood the resulting "holes" left over from mining (even if all overburden were filled back into the former mine, the "missing" coal would mean the surface would still be below the natural
water table) as had been done with what is now
Senftenberger See, the plans for the deep and wide former mine were only seriously made after reunification. After the mine closed on 30 June 1993 exactly a decade of earthworks to ensure
slope stability and eliminate the danger of
landslides followed and flooding started on 30 June 2003. While all open pit mines operating below the natural water table require the lowering of the water table (usually via extensive pumping), simply letting the water table rise naturally is usually not enough to quickly flood the former pit. Besides allowing quick conversion to new uses, quick flooding is also desirable as it reduces the risk and amount of
acid mine drainage (minerals like
pyrite which are stable in
anoxic conditions oxidize if exposed to air, giving rise to
sulfuric acid - this process is slowed or stopped by covering those minerals in water). Thus it was decided to use the nearby
Saale river as a source of water to ensure quick flooding. Flooding was completed by 2011 and the water level in the new lake had risen by per day during flooding. A water level of 98.05 m above
Normalhöhennull was reached on 29 April 2011. However, due to seapage, water from outside sources will probably have to be provided for a further two decades. ==References==