Understanding the ecological evolution of a lake requires a good knowledge of the main physical processes which occur there. The thesis analyses two mechanisms closely associated with the hydrodynamic and thermal behaviour of lake Bourget (France) the density currents, which are driven by the river inflows, and the internal waves, which are generated by wind events. Two approaches have been carried out : field surveys (wind data, temperatures and currents in the lake have been collected) on the one hand, and mathematical modelling on the other hand. Both for density currents and internal waves, the mathematical approaches have been validated for academic cases simplified geometry, thermal stratification with two layers. At the environmental scale, numerical results are in good agreement with most of the observations. Following this study, a coupling with anecological model will be implemented.