For 10 consecutive winters, measurements were carried out in Lake Vendyurskoe, Karelia, Russia. The aim of these measurements was to investigate some of the physical processes in this small shallow lake during its ice-covered period. Detailed measurements of ice thickness and condition, snow thickness, water temperature, salt content, and currents were developed into a database. Within this database are the winters 1994/95 and 1995/96, which are characterized by a very sharp change between positive and negative phases of the North Atlantic Oscillation (NAO). This note investigates and compares the effects of these two NAO phases on the regional climate and their relation to the thermal regime of Lake Vendyurskoe. It became clear that the ice-covered period length did not vary much from one winter to the other; however, a large difference was observed in the maximum average ice cover thickness and in the average water temperature at ice formation ( e. g., larger thickness and colder water temperature during the 1995/ 96 winter).