Mining strongly influences the water quality and the water balance in river basins. This is especially true for large-scale and long lasting opencast mining for lignite. Pyrite oxidation mobilizes huge amounts of acidity, sulphate, iron and other heavy metals. They may impact the quality of ground water, rivers and lakes. Pit lakes are an important part of the post-mining landscape in the Central German lignite mining district. Many new pit lakes formed in the catchment area of river Mulde and river Saale since 1990, besides the older pit lakes in this region. A survey of the pit lakes of the Central German mining district and their water quality is presented. Major mechanisms governing water quality and interaction with river systems are discussed.