The Morskie Oko Lake is the only lake in the Tatra Mountains in southern Poland with regular observations of ice phenomena.On the basis of data from 1971 |-2010 a study on formation, disappearance and duration of ice cover on that lake was carried out.The results show decreasing maximum thickness of winter ice cover and also shortening duration of ice phenomena on the Morskie Oko Lake, while air temperature of the cold season recorded at the same period at Zakopane meteorological station at the foot of the Tatra Mountains shows positive trend.The detected changes, besides significance in the climate change studies, may have important consequences for fish, phytoplankton and zooplankton of the Morskie Oko Lake.Since the duration of ice cover has direct influence on evaporation, this may also affect the water balance of the lake.