The growing energetic demands are promoting new business strategies in the operating of hydroelectric power plants. These are materialized by increasing the role of the reversible plants to produce high quality energy. This fact becomes in an abrupt and quick variation of the water level of the reservoirs. This influences at the temperature levels in the dams. Furthermore, since the dams have been working for years, temperature registers from them are available. This enlarges the initial hypotheses considered in the project calculation. This paper summarizes the results obtained in the enlargement of the operating system involving the Baserca and Llauset dams. The initial experimental data come from the measurements which have been taken in those dams after 30 years of operation.