In December, 2007, after 30 years of operations, the mine of Meirama ceased extraction of brown lignite. Since then operations have begun which will lead to the formation of a big mining lake (~2 km2 surface and up to 180 m deep) after controlled flooding of the open pit. In the process of flooding, both surface and ground waters are involved, each with their own chemical signature. According to the information available, the diversion of surface waters towards the pit hole should lead to the formation of a water body of acceptable quality. However, an unassisted flooding process could eventually form an acidic lake.