Global warming has altered the thermal dynamics of reservoirs worldwide, affecting aquatic ecosystems and water quality. In this work, a hydrophysical simulation is used to evaluate an adaptation strategy for the dimictic drinking water reservoir Lichtenberg in Germany in a realistic operational setup. We ran an ensemble of three 1D lake models coupled with a rainfall-runoff model to simulate the reservoir thermal dynamics until the end of the century under RCP2.6, RCP4.5, and RCP8.5 with the current and adapted management. The ensemble predicted a consistent increase in surface and deep water temperatures, which was highest for RCP8.5 at 0.4 and 0.1 K/decade, respectively. While surface water remained rather insensitive to the adapted strategy, the increase in deep water temperature was counterbalanced by the adaptation of the outflow to the downstream river from the hypolimnion to the epilimnion. Regardless of the simulation period, the adapted strategy reduced deep water temperature by about 1.5 K under all climate scenarios. It also avoided early summer hypolimnion depletion, thereby increasing the availability of deep, cold water for drinking water production.