Velenje Lake

The Saleska lakes are very »young«, as they largely formed after the Second World War. They are certainly the most striking phenomenon in the Saleska Valley.
Velenje Lake, with the Šoštanj Thermal Power Plant in the background. The lakes formed as a consequence of the underground mining of lignite in the Velenje coal mine. The mining subsidences formed in the middle of the basin floor of the Saleska Valley, which had previously been largely in agricultural use, and partly, of course, also settled. The volume of the subsidence basin exceeded 120 million m3 in 2005 and covers a good 6 km² of surface area[1]. Water filled the deepest parts of this basin and three lakes formed. With a combined surface area of more than 200 ha and a volume of over 35 million m³, they are among the larger lakes in Slovenia.

Source: Wikipedia