Abstract: The hydrological characteristics of the upper reaches of the Iskar River are distinguished by significant fluctuations and pronounced seasonality. In these sections of the river an anthropogenic pressure have been detected, which affected on the ecological situation of the aquatic ecosystem. The aim of the research paper was to analyse hydrological characteristics and physico-chemical parameters of the waters at the upper part of the Iskar River. Hydrological data from the conducted own measurements in selected representative sites were collected. An analysis of the water level, water quantity changes for the period 2015-2020 and water balance estimation was made. Water samples from the selected representative sites in the upper part of Iskar River were taken. Water temperature, pH, dissolved oxygen/saturation and conductivity were measured. Ecological status of the studied sites according to the values of the basic physicochemical parameters of the lotic ecosystem was assessed.