Although thermal waters are found in numerous Alpine valleys, the mechanisms responsible for their occurrence remain unclear. The present study used a 2-D numerical model of an Alpine hydrothermal system (La Léchère, Savoie) to investigate these mechanisms. A steady-state hydrodynamic model was calibrated using present-day observations, and then applied to predict outlet temperatures assuming steady-state conditions and the current heat flux and water flow. This simulation produced anomalously low outlet temperatures compared with present-day temperatures, indicating that water circulation within the La Léchère aquifer cannot have been constant throughout its history. Based on the suggestion that glaciations block aquifer circulation, a second simulation was carried out assuming zero water infiltration during the Würm glacial period. The outlet temperatures predicted by this second simulation were much closer to present-day temperatures. These two simulations show that the thermal anomaly at La Léchère is incompatible with the classic model of the progressive heating of thermal waters and that the current temperature of the thermal waters can be explained by changes in aquifer infiltration rates.