Close to Tullamarine Airport, Jacksons Creek (flowing from the west) and Deep Creek (flowing from the north) join to form the Maribyrnong River at Keilor North. The river runs south through Yarraville in inner Melbourne before meeting the Yarra and flowing into Port Phillip Bay. Rosslynne Reservoir near Gisborne is the largest storage in the system and harvests water from the headwaters of Jacksons Creek
Rosslynne Reservoir is the only major storage in the Maribyrnong catchment, and it is located in the upper reaches of Jacksons Creek. The priority river reaches for environmental watering in the Maribyrnong system are reaches 6 and 7 (upper and lower Jacksons Creek respectively), downstream of Rosslynne Reservoir. The release capacity of 20 ML/day from Rosslynne Reservoir is a significant constraint on what can be achieved by environmental deliveries.
The VEWH does not hold an environmental entitlement in the Maribyrnong system and depends on temporary trade to meet demands. Over the past four years, Melbourne Water and the VEWH have worked with local diversion licence holders to purchase unused water that can then be delivered specifically for environmental outcomes in the system. This arrangement is negotiated each year and will only occur with the agreement of all parties involved.