A systematic study was conducted over six years (1994-1999) on a shallow ice covered lake in the Russian Republic of Karelia with the aim of developing better understanding of some physical processes occurring in shallow ice-covered lakes. The average ice-covered period was 182 days while the longest ice-covered period was 193 days. The average lake water temperature at ice formation was 0.5-1.0°C, while the average water temperature just before ice break-up was close to 4°C. The heat flux from water to ice was low during early winter but could increase above 5 Wm-2 (daily average) during the last month before ice break-up. The heat flux from sediment to water was the main source of heat to the water body during early to mid winter being about 2-6 W·m-2 during early winter but decreasing to about 1-2 Wm-2 during early spring.