The paper provides the data about the quantity of beaver ponds, quantity and location of spawning hillocks of passage salmon fishes (Brown trout and Atlantic salmon) on two spawning waterways – the Tartak stream and the river of Dudka (inflows of the river of Vilia, basin of the Baltic Sea). There were estimated the influence produced by quantity and capacity (height) of beaver dams on the results of spawning campaigns. It was ascertained that the building activities of the beavers has significant impact on the conditions of reproduction of salmon fishes: the dams appear to be an obstacle for migration of salmon spawners and the sections of waterways occupied by the ponds get unsuitable for spawning of salmons and thus the spawning areas are reduced.