 During this period, the temperature slowly increases with depth in the lake, being coldest near the ice-covered surface at around freezing, and reaching about at a depth of .After the surface ice breaks up, the surface water is slowly warmed up by the sun, and in May–June, the upper or so becomes homothermic (same temperature throughout) at around because of water mixing.The sun continues to heat up the surface layer, and at the peak in August can reach up to about in the main sections and in shallow bays in the southern half of the lake.