Environmental water has gained significant momentum as an intervention to redress the adverse ecological consequences of river regulation. In many regulated river catchments of Australia’s Murray-Darling Basin, environmental water is delivered as environmental flows to meet predefined ecological targets at selected locations in the system. Such target-based approaches are appealing to policy makers as they purportedly maximise beneficial outcomes by using the least amount of water. However,  there is insufficient evidence of the success of target-based approaches for managing environmental water. Using findings from my PhD study which involved a critical examination of target-based management of environmental water in two catchments of the Murray-Darling Basin, I highlight some of the challenges of using targets for interventions in highly dynamic river systems. I applied ‘boundary critique’-a methodology borrowed from the Critical Systems Thinking tradition- to critically examine the foundational assumptions of the targets chosen for environmental water management in each catchment. I found that targets chosen for environmental water are based on unrealistic assumptions about the influence of extraneous factors. Due to confounding influences, observed outcomes documented in monitoring reports are rarely attributable to environmental flows. Tightly defined targets tend to exclude the interests of many stakeholders, placing at risk the ongoing political commitment to environmental water. Faced with these challenges, must we remain committed to target-based approaches? Or can we explore more open-ended approaches for restoration of river systems?