The objective of this work is to characterize the hydrodynamics and transport time scales of the main hydroelectric generation reservoir in Uruguay based on a numerical modelling approach. The work is based on the analysis of numerical results from a hydrodynamic model implemented for the Salto Grande reservoir, using the TELEMAC-MASCARET Modelling System (TMS). A 2D depth-averaged approach is followed. The model is calibrated and validated using data of surface elevation at several stations along the river-reservoir system. The obtained results show good agreement with the measured data, representing satisfactorily the main features of the Salto Grande dynamics. A simulation with realistic forcings during several years allows us to analyse the circulation in the river-reservoir system, and the estimation of the transport time scales based on numerical experiments with a passive tracer. The effect of the wind forcing is also analysed.