In 2005 Victoria legally designated an environmental water reserve as a start to strategically sharing water between consumptive use and the environment. The accumulation of environmental water and application of environmental flows has occurred in different systems along varying timelines. It is now important to determine whether this sharing of water has had the desired effect in arresting deterioration of waterway ecological health. This paper describes an assessment approach that was developed to account for the potential difficulties, including that: there was no monitoring program specifically designed and implemented for this assessment; existing data collected for other purposes must be used; defining ecological health is complex; each waterway functions uniquely; and, there are numerous non-flow factors affecting ecological health in waterways. Moreover, environmental water management was introduced relatively recently in most systems such that there may not yet be an impact on ecological health or any change may still be small. A hierarchical before-after regression model is recommended given the limitations of the data available. It is recognised that the issues may confound clear assessment and additional evidence will be needed to explain the quantitative findings. This evidence may come from relevant scientific literature, management documentation such as environmental flows studies or environmental water management plans, or short-term monitoring studies targeted specifically at the stream condition-flow connection, which may provide indicative results for understanding of predicting longer term change. The approach aims to be robust while accounting for the limitations, and is presented to stimulate collaborative discussion and obtain feedback.