The paper considers mountain rivers, which usually feature high dynamics of hydrological phenomena. The variability of the Sola river flows in the Polish Carpathians is presented based on water-gauge measurements from the hydrological long-period of 1956-2015. Flows for the upper section of the river, where there are no storage reservoirs, were analysed. A broad range of flows was shown – from 0.59 to 1250 m3/s at a mean flow of 15.5 m3/s. It was also shown that within a year flows grow in the spring (thaw freshets) and summer periods (rainwater freshets). Mainly the summer freshets are dangerous, consisting in a sudden rise of the flow due to rains. This is shown by high values of maximum flows in June and July. In the case of mountain rivers, such as the Sola river, it is necessary to undertake actions stabilising the flows, which on the one hand have flood-prevention importance, and on the other hand protect water resources in long dry periods. Actions should be concentrated on proper arrangement of the catchment area, slowing down the rainwater outflow. A proper land use is especially important (distribution of forests, of arable and developed areas) depending on the land elevation above the sea level and inclination, as well as small storage facilities creation.