The surveys were carried out in OnezhskoyePomoryeNational Park, which in 2016 was joined to KenozerskyNational Park(Arkhangelsk Region). Four streams 6 to 13.6 kmlong were surveyed. The occurrence of the Salmo trutta in different areas across the watercourses and the habitat conditions were assessed. Juvenile and adult brown (resident) and sea (anadromous) trout aged 0+ to 6+ were detected. Data on the age composition of the trout are reported, the share of precocious males and the distribution density of juveniles of different age classes were determined for all the surveyed streams. The captures of precocious males and a precocious female confirm the high plasticity of the species in rivers emptying to theWhite Sea, which is manifest in the presence of both resident and sea-going individuals within the same population or reproductive group. The actions required to conserve and enlarge the trout population in streams of the national park include clarification of the timing and conditions of the spawning migration, investigation of the dynamics of the downstream migration of smolts, surveys of their abundance, as well as more intense protection of the watercourses.