Expectations from the community to demonstrate the effective use of environmental water to delivery ecological outcomes have increased with the making of the Murray Darling Basin Plan and the legacy of the millennium drought. The Commonwealth Environmental Water Holder has been established (in 2008) to make decisions on using the Commonwealth environmental water holdings to protect and restore environmental assets in the Basin. This paper describes the management of Commonwealth environmental water through active decision making that utilises emerging science and expert knowledge (scientific and operational) to maximise environmental outcomes whilst minimising risks and unintended impacts in a complex operating environment.

 Since 2008, the type and scale of environmental watering actions have evolved. With the continuing growth in the Commonwealth environmental water holdings and increased understanding of watering requirements of ecosystems, the management of environmental water to deliver environmental outcomes has needed to improve. A recent focus has been on river flows targeting native fish recruitment and inundation of fringing wetlands. Efforts are being made together with river operators, state delivery partners and other environmental water holders to coordinate the timing of environmental water delivery across multiple catchments within the southern connected basin and to innovatively apply operating rules to support environmental outcomes across the basin including increasing longitudinal connectivity within the River Murray.

Watering actions are actively managed together with delivery partners, drawing on real- time monitoring of river conditions and ecological responses such as native fish spawning and the activity of waterbirds, at local and regional scales. Active decisions to suspend, extend or otherwise modify actions are often made to maximise ecological outcomes and minimise risks. Targeted intervention monitoring ecological outcomes is helping managers to learn from experience and refine watering actions over time. Evaluation of the growing body of monitoring data is ongoing and is being used to demonstrate the outcomes of the use of Commonwealth environmental water and how it is contributing to a healthier Basin.
Many challenges remain, including managing risks and impacts to third parties, planning in the context of a highly variable and unpredictable climate, and working within existing river operation rules and protocols not designed for environmental watering. In the case of monitoring and evaluation, challenges exist in collating and understanding outcomes at the basin scale, transferring knowledge and inferring outcomes in catchments without monitoring in place and understanding the reasons and implications of cases when expected outcomes are not achieved.