During summer seasons of 1982 and 198S the authors collected observations on rate of soil thawing under and around shallow tundra lakes. Two lakes were studied: A on the terrace 10 m a.s.1. in northern Kafliöyra whereas B at about 40 m a.sJ. in southern margin of Sarsdyra. The lakes indicated considerable variation of water lavels (10—20 m) caused by limited water bodies (to 40—80%) at the end of the observation period. Soil thawing was studied in sections across lake basins and to 20 m around them. A thawing rate was found greater under the lakes than in their surroundings and it was noted to be in the same time the quicker the larger was the lake. Studies of the lake B proved also that increase in the reservoir depth made a greater rate and depth of summer thawing. This process varied also considerably in time. At the beginning of a polar summer the dry soil of elevated tundra thaws sooner while permafrost under water reservoirs gets conserved. Later on (in August) a quick aggradation of active layer in noted under the lake. A heat accumulated in water bodies prolongs the soil thawing as well.