The article reports the results of an experiment to assess the geothermal potential of the territory based on measurements of water reservoirs’ bottom temperatures.The research was conducted in 2021 on Bolshoy Solovetsky Island, which, according to some data, is characterized by the presence of geothermal anomaly on the one hand, and has a large number of lakes on the other. For lakes with depths greater than 5 m, the results of temperature measurements indicate that the temperature profiles correspond to the dimictic type of lakes – with two periods of circulation in spring and autumn. During the experiment, abnormal values of bottom temperatures at depths of more than 15 m were detected in Lakes Bolshoe Krasnoe and Shchuchye: 5.16–5.26 °C for Lake
Shchuchye, and 6.16–6.56 °C for Lake Bolshoe Krasnoe. The possible causes of these anomalies are discussed including: chemical reactions in the near-bottom sediment layer, increased heat flow in the upper part of the Earth’s crust, and wind mixing in the lakes. Recommendations are given for further study of the anomalies in order to clarify their nature.