Flows through the Yarra system have become highly regulated due to the construction of water storages that capture natural run-off and allow the controlled removal of water for consumptive uses. Over time, the lower Yarra River has been straightened, widened and cleared of natural debris as Melbourne grew around its banks, with the earliest alterations to its course occurring as far back as 1879. Environmental watering aims to reinstate flows that support ecological 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 (see below) and delivery of water to these reaches is also expected to achieve flow targets in neighbouring reaches. The environmental flow reaches in the Yarra system are shown in the below map. 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 Diamond Creek, Plenty River and Merri Creek) provide additional water to the Yarra River.