A methodology based on the use of time-lapse photographs is presented to evaluate the leakages over time of a reservoir (Montejaque dam, Málaga Province, Spain) that feeds a karstic aquifer. In particular, photographic control allows the evolution of water levels in the dam and the river that feeds it to be monitored. Through changes in water volume, which are calculated from the level differences, daily leakages are evaluated, and the relationship between leakages and the water level of the reservoir is established. The proposed method includes adjusting the hydric balance and the use of digital terrain model and climate data. The inputs (river flow and direct precipitation) and other outputs (direct evaporation) are also evaluated. Values between 4 m3/s and 0.35 m3/s are obtained for the reservoir infiltration, clearly superior to the values obtained at the time of the construction of the dam in the 1920s. Mobilisation of the filling of fractures and conduits in karstic massif and calcite dissolution are processes that can influence this behaviour. When the water level is very low, the obtained values are below the historical leakages due to deposition of clay sediments at the reservoir bottom.