The filling and emptying cycles of reservoir operations may change hydrological mass loading, leading to a flexural deformation of the crust that may compromise the infrastructure safety or trigger earthquakes. In this study, we investigate the seasonal crustal response of the Tehri reservoir in the Garhwal Himalaya, northern India, using interferometric synthetic aperture radar (InSAR), Global Positioning System, the Gravity Recovery and Climate Experiment, radar altimetry, and in-situ water-level measurements. Results show that the evolution of vertical ground deformation is modulated elastically by the reservoir operation, whereas the horizontal displacement measured near the reservoir exhibits a time lag of ∼65 days with respect to the vertical displacements and water-level variations. The delayed deformation transients indicate that the reservoir loading/unloading cycles affect the near-surface hydrology in its neighborhood. The broader distribution and higher amplitude of ground deformation during the loading periods revealed by the InSAR time series can be explained by water-rock interactions, which cause a decrease in the effective Young's modulus within the top 300-m crustal layer. Our results demonstrate the potential of using space geodetic data to ensure a better understanding of the solid Earth response to regional hydrological changes.