This study aims at determining the dendrochronological indicators of a changing snow accumulation regime on an island of a recently created reservoir in northern Québec. Reservoir Robert-Bourassa (LG-2) is a vast lake (2,835 km²) covered by ice from mid-December to mid-May. Snow drifts across the frozen lake until it is trapped by obstacles on islands and at reservoir margins. Pre-established trees on the islands are negatively affected by the local augmentation of snow accumulation. Changes in tree growth forms of a severely exposed forested island indicate that damage occurred soon after reservoir filling. At the island edges, the decay of trees increases the wind exposure of border trees, causing massive foliage loss, thus reducing tree growth. Beyond the edge, in the island interior, drifted snow accumulates due to the wind breaking effect of the shoreline trees. Since reservoir filling, incidents of stem breakage, shoot bending and tilting, and branch tearing have increased due to snow packing. Such anomalous growth features appeared during the first 3 y after reservoir filling. Tree rings also indicate the trauma of wind and cold exposure stress. Such stress results in the incomplete formation of annual rings and the development of a series of resin ducts. The amount of snow packing damage to trees depends on the abundance of snowfall and on winter levels of the reservoir. The combination of these two factors controls the amount of snow reaching the island forests when drifted by the wind.