The article discusses the role of the Green Belt of Fennoscandia (GBF) in the dispersal of beavers. The study is focused primarily on old-growth forests inside GBF, which have been preserved in the Kostomukshsky Strict Nature Reserve and Kalevalsky National Park. The specific characteristics of these areas – the abundance of waterbodies and the ex-tremely poor food resources for beavers – accelerated the dispersal of Canadian beavers from Finland towards the east and south of Karelia. Aspen, birch and willow, on which beavers mostly feed in winter, rarely occur in the north of GBF and are consumed by beavers in the first 2–3 years of their stay at a waterbody. The animals are therefore im-pelled to change their places of residence frequently and move over long distances. Surveys carried out in the Kostomukshsky Nature Reserve in 2018 showed that over 80 % of known colonies have been abandoned by beavers. In 2001, this proportion was 60 %. Most of the inhabited colonies were re-occupied, as a rule by single animals, who settled in an abandoned lodge temporarily. On average, the share of settlements occupied by single beavers was 45 %. The distribution of beaver settlements in old-growth north-taiga forests is very uneven, since it is more dependent on forage resources than on favorable habitat. It our surveys, 73.3 % (n = 75) of the settlements were situated in river stretches with water-logged birch and birch-spruce forests growing along their banks. A half of all settlements situated at watercourses were concentrated near highways, railways, power lines, i. e. where aspen and birch stands have formed after logging. We revealed a high building activity of beavers living in the north.