Popovo polje covers an area of about 4,000 ha of soil and is situated in the region of Herzegovina karst (Yugoslavia) with favourable climate conditions. Like most of the karst terrains it is part of the karst depression, later filled in the course of alluvial-colluvial processes. After the construction of the water-power plant there appeared positive changes of the natural hydrologic regime. This paper also presents the course and the nature of these changes as well as the results of the transformations in agriculture in the observed region.