Blidinje lake, or more commonly just Blidinje, is the biggest mountain lake in Bosnia and Herzegovina. It is situated in Herzegovina, between the mountains Vran and Čvrsnica, at an altitude of approximately 1,180 m. Some publications refer to it as a glacial lake. Although undoubtedly there is evidence of the prior existence of glaciers and glacial relief in the area around the lake, the morphology of the lake’s bottom and shores, changeability of the surface, and a number of records on the lake’s origin challenge the theory of the lake’s glacial origin. The aim of this paper is to use cartographic sources of spatial data, historical records, geomorphological analysis, existing literature and interviews with the local population in order to determine how and when Blidinje lake was formed. The methods used in the paper are the analysis of the available written and oral sources, geomorphological analysis, the analysis of old maps, and the analysis of toponymy. The existing historical and contemporary maps were used to perform lake surface measuring in GIS environment. All data acquired were used to disprove the glacial origin theory and to provide evidence that the lake was formed artificially by the end of the 19th century.