There is a confusion of ways to determine the environmental flows required to sustain rivers and wetlands environmental values. For the last couple of decades, Australian governments have used a variety of techniques to plan and implement environmental flows in the Murray-Darling Basin to optimize the environmental, social and economic outcomes from the use of water resources. One of the common features of these approaches has been the use of species and communities environmental flow requirements. As implementation of the Basin Plan has proceeded, it has become apparent that in addition to flow requirements, in some situations consideration needs to be given to elements of a flow regime that constitute a threat. Some of these flows are relatively well understood, for example, declining water levels during waterbird breeding and oxygen depleted water returning from floodplains. Others, including seasonal reversal of flows remain uncertain threats. This presentation will discuss ways in which flow threats became apparent during environmental flow assessments and their implications for environmental flow management.