Map of Werribee River system: click to enlarge.
Overview of 2025/26
The delivery program operated to the dry scenario (Seasonal Watering Plan 2025-26) during winter/spring and early summer/autumn to present. This was due to flow conditions reflecting rainfall and streamflow deficits accumulated from summer/autumn in the previous water year.
Dry conditions experienced in summer/autumn 2025 continued into winter and early spring. During winter, mean maximum temperatures were above average across the catchment, with rainfall and streamflow below average (Melbourne in Winter 2025).
Above-average monthly rainfall totals were accumulated at the end of October through November, leading to the spring season ending with above average-rainfall totals (Melbourne in Spring 2025). However, this masked underlying rainfall and streamflow deficits experienced throughout most of the season which aligned with the dry operating scenario.
Environmental water delivered in 2025/26
In accordance with the Seasonal Watering Plan, environmental water was delivered to Pyrites Creek from Merrimu Reservoir (reach 6) to achieve three spring fresh events.
These flows played a crucial role in supporting the growth and recruitment of riparian vegetation. Furthermore, they contributed to flushing silt and scouring biofilms, thereby improving water quality. Importantly, these actions improved habitat and migration opportunities, benefiting native fish, frogs, and waterbugs within the ecosystem.
A series of 3 summer/autumn freshes are planned for reaches 8 and 9 (lower Werribee River), of which 1 has been delivered to date.
Delivery of these freshes has seen a general improvement in water quality parameters in the lower Werribee, along with the dispersing of blue green algae blooms from the system during and after the event.
More generally, the freshes provide a range of benefits such as:
- promoting the growth and recruitment of water-dependent streamside vegetation
- flushing silt and scour biofilms and algae from substrates on the stream bed
- maintaining pools and channel dimensions
- maintaining habitat connectivity for native fish, frogs and platypus.
Reach 8 has also benefited from increased flows as a result of irrigation deliveries made by Southern Rural Water from Melton reservoir, allowing some partial achievement of winter/spring and summer/autumn low flow targets.
Key environmental values
In the Werribee River system, water for the environment supports the following key environmental values.
Opportunities for shared benefits are also incorporated into planning and watering decisions, if they do not compromise environmental outcomes. We are currently planning to undertake a Cultural Values Assessment for the Werribee River with Wadawurrung and Wurundjeri Woi Wurrung Traditional Owners.
Potential watering actions
We plan for all climatic scenarios. Below are the proposed environmental watering actions for the Werribee River in 2026/27 under an ‘average’ year scenario:
- Spring freshes (reach 6 - Pyrites Creek)
- Winter/spring/summer low flows (reach 6 - Pyrites Creek)
- Summer/autumn freshes (reach 9 - lower Werribee River & estuary)
- Winter/spring freshes (reach 9 - lower Werribee River and estuary)
- Summer/autumn low flows (reach 9 - lower Werribee River and estuary)
- Spring high flow (reach 6 - Pyrites Creek)
