Hydropower resources are regionally and are differentiated periodically. They depend on natural or regulated flows and water levels and factors causing their periodic changes, fouling and icing the river bed. The main problem of working hydropower in the winter is creating a ice form restricting the flow water to the intake inlets. Beginning of the freezing period depends on meteorological factors, air temperature, snowfall, associated with the operation of water facilities, temperature, water discharges and usage of floating baffles in areas where the water has the lowest speed. The article presents an analysis of the parameters used in the assessment of energy resources of rivers. To determine the prevalence of forms and periods of ice phenomena used historical hydrological data, and reduction factors determined by analyzing water levels and flows. Winter reduction factor is calculated by riverbed bandwidth curves, referring to winter flows obtained from the baseline curve. Analyses include selected sections of lowland rivers, where ice cover has occurred causing changes in the major hydroelectric curves.

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