The risks associated with the sedimentation of the Red Lake. In 1837 in the metamorfico-mezozoic zone of the Oriental Carpathians happened a relatively rare phenomenon, the slope sliding of the Ghilcos Mountain blocked the Bicaz River and formed a natural barrage lake which received the Red name later. The sedimentation of the lake is a natural phenomenon, which can not be seen as a risk process. But if the silting reaches a rhythm which exceeds the natural and endangers the goods or the activities because of some natural or/and anthropical factors, it will become a risk phenomenon. In the case of the Red Lake, we consider that it had extended to such a state and rhythm that the phenomenon stepped into the category of the natural risks. Although the phenomenon isn’t so spectaculous like the tornadoes, the tsunamis or the landslides, the losses which will appear because of the disappearance of the lake, must be seen as the consequences of a natural risk phenomenon. So investigation, forecast and defense against this is necessary.