In the present study we have set to highlight some interesting aspects regarding spatial and time distribution of heliotherm phenomenon in one of the most representative lakes in Romania, namely Lake Ursu (Bear) in Sovata. After some details regarding natural processes of existence and evolution of the mentioned lake, we have presented a few methods and techniques used in data collection and analysis. The extended period of time (nearly 10 years) of the current research, combined with the ones achieved before, have made it possible to interpret the heliotherm phenomenon in many ways: on short-term (daily), seasonal and multiannual one, for mid and long-term. We can observe a clear dependence of the intensity of the phenomenon not only on solar radiation but also on salt distribution, season and anthropic influence. Also, in contrast to the beginning of the 20th century, an unquestionable decrement of the phenomenon over time can be seen. Using GIS model in the case of Lake Ursu has made it possible for the identification of the heliotherm horizon not only in longitudinal but also on three-dimensional profile. The conclusions reveal the necessity of taking some measures to protect lacustrine environments and the perpetuation of the heliotherm phenomenon by using better ways of extracting resources and doing seasonal surveys.