<p>Hydropower plants operated on demand cause rapid and frequent flow fluctuations (hydropeaking), which negatively impact downstream ecosystems. However, an improved understanding of the ecological effects of hydropeaking and confounding riverine stressors is needed to provide benchmark knowledge to mitigate impacts of hydropeaking. To this aim, multi-scale approaches are needed to better understand ecological processes. This article synthesizes key advances in our understanding of flow-ecology relationships in hydropeaked rivers at the national and the river bar scale, integrating data-driven, field, and experimental approaches, all targeting fish as an ecological indicator. These findings are placed in the context of hydropeaking mitigation by highlighting ways to bridge the gap between science, management, and policy. The article also points to urgent research questions, particularly regarding recurring hydropeaking events.</p>