Integrating dispatchable hydropower with nondispatchable photovoltaic (PV) power is a promising way to enhance resource use efficiency. However, hybrid generation of these energy sources may exert greater pressure on the integrated water resources management, calling for reservoir reoperation. To address this issue, we propose a procedure to derive adaptive operating rules for a large hydro—PV hybrid power plant consisting of following steps: (1) establish a short-term simulation model to estimate the PV curtailment rate arising from specified long-term hydropower output, in which the relationships are represented as PV energy-loss functions to bridge long- and short-term operations; (2) design six operating rules that incorporate the PV energy-loss functions to simulate the system's long-term operation; and (3) develop a multi-objective optimization model to identify the most effective operating rules. A case study was carried out for China's Longyangxia hydro—PV hybrid power plant. Results showed that, compared with traditional operation, the average annual energy production and power supply reliability of the optimal rule curves increased to 7.3 billion kWh (4.3%) and 90% (47.5%), respectively, while the water shortage index decreased to 114 (6.6%). The derived operating rules could achieve good balance between PV integration and water management.