ABSTRACT: Hydrogeological structure of dolomites and limestones around the Kopa Mt. (1187 m a.s.l.), occupying area of 15.538 km2 and belonging to the hronicum unit in the NW part of the Veľká Fatra Mts., was for several decades supposed to be rich enough in infiltrated precipitation. According to this assumption, hidden surpluses of groundwater flow into the alluvial fan, surface waters of the Krpeľany water reservoir and maybe also feeding of the deep groundwater circulation were expected owing to the results of preliminary water balance calculations. However, detailed studies based on the results of thorough hydrogeological mapping on the 1 : 10,000 scale level, hydrometric investigations of the surrounding small streams and thermometric and resistivimetric measurements of the Krpeľany dam surface water had revealed, that the water balance in the area is without any major hidden groundwater outputs from the structure. Even the more recent evapotranspiration studies support this result.