Evaporation trends in the stable isotope composition (¹⁸O/¹⁶O, ¹⁷O/¹⁶O, ²H/¹H) of throughflow ponds in a hydrologically complex and seasonally dynamic lake system can be reliably predicted by the classic Craig–Gordon isotope evaporation model. We demonstrate that the novel ¹⁷O-excess parameter is capable of resolving different types of evaporation with and without recharge and of identifying mixing processes that cannot be resolved using the classic δ²H–δ¹⁸O system alone.