How much can we alter a river’s flow regime without causing ecological impacts? Are there critical thresholds of change that must be avoided? These questions have been put to me by water managers throughout my environmental flows career, and no doubt to many members of this audience. This presentation will explore evidence from a trial of the framework called ELOHA (Ecological Limits of Hydrologic Alteration) in south-east Queensland, with emphasis on fish responses to changes in flow regime downstream from dams. It will interpret impacts on fish assemblage structure and individual species in relation to habitat preferences, diet and reproductive strategy. These findings will be compared with evidence from international studies in an effort to seek concordance of flow regulation impacts, with emphasis on fish life history models. Finally, how has ELOHA contributed to water management policies, particularly the concept of a precautionary safe and just Earth System Boundary (ESB) for surface water use at basin scales? Can we strengthen the existing precautionary safe and just ESB for surface water in terms of limits to changes in the magnitude, seasonal timing, frequency of occurrence, rate of change, variability and predictability of river flows?