Dams are critical, interdependent elements of society’s water infrastructure. As that infrastructure ages and environmental values and laws change, the management and operations of dams and reservoirs are also changing. These changes pose news challenges in, and highlights interactions between, the engineering, ecology, law, and socio-economics of dams. This seminar will emphasize the uncertain but critical interactions that make dams an archetype of complex systems. First, current research on the science, management, and community of dam removal will be introduced, with emphasis on how science is informing management, policy, and engineering design. Next, research on the reoperation of reservoirs under climate change will be presented, including the application and limitation of models and decision frameworks. Finally, other relevant examples (e.g. fish passage, environmental flows, sedimentation from wildfires) of complex interactions at dams will be briefly discussed. The seminar will close with motivations for teaching and research on the engineering of complex hydrosystems.