WTP after Floods
In short:
EPA Victoria has released landmark results from its 40-year Port Phillip Bay water monitoring program, showing key quality indicators are at their best since testing began in 1985. Ammonia levels offshore of Werribee’s Western Treatment Plant have fallen 78 per cent since 1990, with Melbourne Water crediting sustained upgrades and improved technology at the facility.
Forty years of cleaner water
Ammonia levels in Port Phillip Bay waters offshore of Werribee’s Western Treatment Plant have fallen 78 per cent since 1990 — one of the standout findings in a landmark 40-year water quality report released by the EPA Victoria on Tuesday, 9 June 2026.
The result, published to coincide with World Ocean Day, reflects decades of engineering upgrades and process improvements at the plant, which sits on the city’s western fringe and treats roughly half of Melbourne’s sewage.
Melbourne Water’s Executive General Manager of Service Delivery, Sue Jackman, said the Werribee figures demonstrated the value of sustained investment.
“The improved ammonia levels highlight the impact of sustained upgrades, improved technology and smarter processes at the Western Treatment Plant,” she said.
“We’ll continue modernising the plant so the bay remains healthy, resilient and safe for the community and for the precious environment the bay sustains.”
The ammonia improvement is part of a broader picture of recovery across Port Phillip Bay. EPA scientists — who have monitored the bay six times a year since 1985, making it the longest continuing coastal monitoring program in the state — say key water quality indicators are now better than when testing began, despite Melbourne’s population growing by 75 per cent and the urban footprint tripling over the same period.
Testing Forty Years in the Making
The monitoring program, which also runs in the Gippsland Lakes and Western Port, involves teams deploying sophisticated sensors and water sampling equipment from boats at regular intervals across the bay. Results from the Port Phillip program have been published in the international scientific journal Marine and Freshwater Research.
EPA’s Water Operations Lead, Dr Kelly Zuccala, said the science captured both the pressures of growth and the gains from better practice.
“A lot has changed in the past 40 years — our climate has become more variable, inflows have declined, the population has grown by 75% and the urban footprint has tripled,” Dr Zuccala said.
“But our own behaviour, technology and practices have changed too. Wastewater treatment is far more effective at removing many traditional pollutants than it was 40 years ago. And more businesses and residents understand the impact of what they dispose of down the drain or gutter.”
What the Data Shows
Across the bay, suspended sediments have fallen 45 per cent since 1985 — a positive sign for seagrass and other aquatic plants that depend on light penetrating through clear water. Phosphate concentrations have dropped between 30 and 42 per cent depending on location, reducing the risk of algal blooms. Salinity has risen slightly, by around 1.5 parts per thousand, reflecting lower river inflows and greater evaporation driven by climate change.
Dr Zuccala said the four decades of continuous data were essential to understanding long-term environmental trends.
“Our 40 years of continuous testing helps us understand how these climate-driven pressures and system responses are playing out over time.”
The Western Treatment Plant has long been a significant piece of infrastructure for the Wyndham area, and recent upgrades to local sewerage infrastructure — including a pumping station upgrade in Werribee — form part of the broader network that feeds into the plant.
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