Аннотация:Population structure of Mikizha, Salmo mykiss of the Utkholok River (Western Kamchatka) was studied. The abundance of the anadromous form has decreased compared to 1971-1972. As a result, substantial changes in the structure of population occurred. Abundance of the coastal and riverine forms has increased, and females were observed in the river form for the first time. The proportion of repeatedly spawning individuals has increased, and the majority of first spawning. A previous suggestion that different forms of Mikizha of the Utkholok River represent one stock and spawn together was supported. In centain conditions, they can transform to each other as the components of a dynamic system.