Environmental Water Release for the Werribee River system

Melbourne Water, in partnership with the Victorian Environmental Water Holder (VEWH) and Southern Rural Water, will release water for the environment to Pyrites Creek and the Lower Werribee River system on 1 November 2017.

Otherwise known as a “spring fresh”, the release of water will help improve waterbug and frog habitat along Pyrites Creek and provide cues for fish to move in the Lower
Werribee River.

The Werribee river requires a variety of flows to be healthy and this release mimics a short, elevated spring water flow that would previously have occurred naturally after a
spring storm. The river has been highly modified for human use and these flows no
longer occur naturally.

For Pyrites Creek, the water release will provide habitat for frogs and waterbugs, increase the health and growth of plants and scour silt and sand from the shallows of the creek. For the Lower Werribee, it will provide prompts for native fish to move so they can feed and breed for species such as galaxiids, smelt, shortfinned eels and
Australian Grayling. It will also increase the diversity of plants on the river’s edge.

Australian Grayling were recorded for the first time in many years in the Lower Werribee during spring 2016 and autumn 2017 following releases of water for the environment.

The fish spawn in the freshwater reaches of the system before the eggs and larvae drift out to sea. The juvenile fish spend approximately six months in the sea before they
migrate upstream during this spring release of water.

Water for the environment improves the health of rivers and also increases recreational opportunities for the Victorian community.

Melbourne Water will release water for the environment during early November from Merrimu Reservoir and Melton Reservoir into the Pyrites Creek and Werribee system, to improve water flow along the river. Around 1,200 million litres of water will be released during this time. The release will be made in conjunction with Southern Rural Water who manage the reservoirs.

Domestic and irrigation water will not be impacted by this release. The peak event along Pyrites Creek will be from 1st November to 8th November and then will maintain a steady low flow for the remainder of the month. Along the Lower Werribee river, the peak event will be from the 1st November to 10th November.

Changes of river level up to 40cm may be observed which is within normal range. There is a small chance that flushing sediment will increase turbidity (i.e. a cloudy
appearance in the water), however if this does occur it will be temporary and will not have an adverse impact on the river. This type of effect is part of the river’s natural
process and typically occurs during increased flows and storm events.

We will monitor the river levels closely during and after the release to ensure appropriate water quality is maintained. The rate of water being released will be
adjusted if necessary.

During this release, river levels in the area immediately downstream of the Reservoir will be higher than normal and flows will be faster. Melbourne Water is working with the VEWH and other stakeholders to closely monitor the health of the river and aquatic life following the event to inform future releases of water for the environment. This release is in line with the VEWH’s Seasonal Watering Plan 2017-18.