The risks posed by the freezing phenomena on the rivers Tarnava Mare, Tarnava Mica and Niraj in the Transylvanian Subcarpathians and the neighbouring mountainous area. Together with the other risks which exist in a Hydrographical Area, the risks posed by winter phenomena (ice bridge, floating ice, thaws) have their own well determined importance. Because they are in an area which characteristically has colder winters, but also a high relief energy, the way the rivers Tarnava Mare, Tarnava Mica and Niraj behave in the mountainous and submountainous area, is under the influence of the mountain, of low temperatures and long winters. The influence of winter phenomena directly affects the outflow, the morphology of the river bed and the biotic environment. It also affects man, directly as well as indirectly. In what follows, we shall discuss the influences of these phenomena on the environment.