This study highlights reservoirs, which are widespread and expanding human made systems, as significant sources of nitrous oxide, with important implications for climate policy and water management. It provides a major advance by directly quantifying nitrous oxide production pathways in eutrophic reservoirs. Addressing key issues of climate change, water quality, and greenhouse gas emissions, the work is both timely and highly relevant. Conducted in Mediterranean systems, it also offers valuable insights for regional and global understanding of human impacts on biogeochemical cycles.