A computer three-dimensional (3D) hydrothermodynamic model was designed for refined description of intra-annual temperature stratification in deep freezing Lake Teletskoye. The work is aimed at testing this model through simulation of a complex hydrophysical phenomenon, i.e. spring thermobar for real conditions of Lake Teletskoye. In June 2018, while performing field observations of temperature stratification in Lake Teletskoye, a thermobar (stretching from the mouth of the Chulyshman River at the lake’s southern tail up to its deep-water part) was detected and studied. Using the constructed 3D model of thermal regime and actual input data for 2018, the estimate of spring-summer thermobar in the water body as well as the comparative analysis of numerical simulation results and field observation data were made.