Climate change is predicted to affect the future supply and demand for water resources. Current water management practices may not adequately cope with the impacts of climate change on the reliability of water supply, flood risk, health, agriculture, energy generation and aquatic ecosystems. Water managers can adapt to climate variability by structural change, such as increasing the size or number of dams, building desalination plants and transferring water between catchments; however, a broader set of alternatives with multiple beneficial outcomes for society and the environment should be explored. We discuss how modifying dam operations, ‘dam reoperation’, can assist with adaptation to climate change and help restore ecosystems. The main operating purpose of a dam (e.g. flood management, hydropower or water supply) will influence dam reoperation strategies. Reoperation may require integration across sectors or involve multiple dams, enhancing benefits such as water supply or hydropower while simultaneously achieving ecosystem restoration. We provide examples of lessons learned during extreme scenarios (e.g. floods and droughts), where operational flexibility has been demonstrated. We contrast structural climate-change adaptation strategies (e.g. building new dams) and their resulting detrimental environmental outcomes with dam reoperation, which can maximise benefits for ecosystems and society.