The environment is being increasingly recognized as a legitimate user of water. However, tension between environmental and consumptive uses remains and environmental water allocations may be subject to legal challenge. Current predictions of ecological response to altered flow regimes are not sufficiently transparent or robust to withstand such challenges. We review the use of causal criteria analysis to systematically review ecological responses to changes in flow regimes. Causal criteria analysis provides a method to assess the evidence for and against cause-effect hypotheses. Relationships supported by sufficient evidence can inform transparent and robust environmental flow recommendations. The use of causal criteria analysis in environmental science has been facilitated by the development of the Eco Evidence method and softwareâ¿¿a standardized approach for synthesizing evidence from the scientific literature. Eco Evidence has thus far been used to assess the evidence concerning responses of vegetation, fish, macroinvertebrates, and floodplain geomorphology to changes in flow regime, and provides a robust and transparent assessment of this evidence. There is a growing movement internationally to shift from experience-based to evidence-based methods in environmental science and management. The research presented here is at the leading edge of a fundamental change in the way environmental scientists use evidence.