The Yarra River flows west from the Yarra Ranges upstream of Warburton and through the Yarra Valley. It then opens out into a wider plain as it meanders through the suburbs and city of Melbourne before entering Port Phillip Bay. The Upper Yarra Reservoir, O'Shannassy Reservoir and Maroondah Reservoir harvest water from headwater tributaries and a pump station at Yering is used to divert water from the Yarra River to Sugarloaf Reservoir.
Flows through the Yarra system have become highly regulated due to the construction of major water storages that capture natural run-off and allow the controlled removal of water for consumptive use. Over time, the lower Yarra River has been straightened, widened and cleared of natural debris as Melbourne has grown around its banks. The earliest recorded alterations to its course date back to 1879. Environmental watering aims to reinstate flows that support ecological processes and environmental outcomes throughout the length of the system.
Environmental water can be released from the Upper Yarra, Maroondah and O'Shannassy reservoirs. Priority reaches for environmental watering are reaches 2 and 5 and delivery of water to these reaches is expected to also achieve flow targets in neighbouring reaches. Figure 3.2.1 shows the environmental flow reaches in the Yarra system. In the upper reaches, the system is influenced by tributaries (such as Woori Yallock Creek, Watts River and Little Yarra River). In the lower reaches, urbanised tributaries (such as Olinda Creek, Mullum Mullum Creek, Diamond Creek, Plenty River and Merri Creek) provide additional water to the Yarra River.