Strip mining brings about the transformation of the land surface as well as quantitative and qualitative changes in water resources. Strip mining of lignite in the region of Łęknica (SW Poland) has resulted in the formation of the largest anthropogenic lake district in Poland. As a result of lignite mining in the areas, which are galcitectonically disturbed, numerous isolated open casts are formed on the surface of the earth, which after the end of mining often get filled with water and form the characteristic anthropogenic lake districts. It consists of more than 100 reservoirs of the area ranging from 0.01 to 20.20 hectares, which are spread over the area of approximately 40 hectares. In order to study the effect of lignite mining on the land and water environment detailed hydrographic, geological and chemical examinations were carried out within a selected reservoir of the above mentioned lake district. The examinations revealed that lignite mining resulted in the formation of reservoirs and changes in the water relations and then consequently led to the degradation of water quality, which consists among others in the acidification of surface waters up to the pH value of 2,5 and in the enrichment of underground waters in iron and sulfates.