Despite Melbourne’s rapid growth, expanding suburbs and mounting climate pressures, new long-term data from EPA Victoria shows Port Phillip Bay is in better shape across several key water quality measures than it was four decades ago.
The findings come from the state’s longest-running continuous coastal monitoring program, which has tested Port Phillip Bay six times a year for 40 years. The program also runs in the Gippsland Lakes and Western Port.
The results from Port Phillip Bay have now been published in the international scientific journal Marine and Freshwater Research.
They point to a notable public interest outcome: even as Melbourne’s population has surged and the city’s urban footprint has expanded, major indicators including suspended sediments, phosphates and ammonia have improved.
The monitoring work is detailed and highly coordinated.
Out on the bay, EPA scientists lower specialist equipment into the water to measure temperature, salinity, dissolved oxygen, pH, chlorophyll and turbidity — a measure of how cloudy or clear the water is.
One device, known as a CTD, is worth more than $75,000. At the same time, scientists use a Niskin bottle to collect water samples for later laboratory analysis. The sensor readings and samples must be taken at the same depth and time, making precision essential.
That routine has been repeated across decades, creating one of Victoria’s most valuable long-term environmental records.
Climate change remains a major pressure on the bay, particularly through reduced inflows and higher evaporation. But EPA’s Water Operations Lead, Dr Kelly Zuccala said improved industry practice had helped offset pressures from rapid suburban growth.
“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 says.
“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,”
“Our 40 years of continuous testing helps us understand how these climate-drive pressures and system responses are playing out over time.” she said.
EPA’s monitoring program tests surface water for salinity, dissolved oxygen, suspended sediments and nutrients such as nitrogen, phosphorous and silicon.
Across those measures, the long-term trend is encouraging.
Since 1985, suspended sediments have fallen by 45%. That matters because high sediment levels can damage aquatic plants, including seagrass, by blocking light from penetrating the water.
Phosphate concentrations have also dropped by 30 to 42% depending on location. High levels of phosphate and ammonia can contribute to algal blooms, which can affect marine life, water quality and public use of the bay.
Salinity has risen slightly, by about 1.5 parts per thousand, indicating lower river flows into the bay and greater evaporation.
Port Phillip Bay Swim Risk Checker
Check a live rain-based swim-risk estimate for popular Port Phillip Bay beaches. This is not the official EPA Beach Report, but it can help flag stormwater risk after rain.
General guide: avoid swimming near stormwater drains, in murky water, or for 24–48 hours after heavy rain. For official advice, check EPA Victoria’s Beach Report.
Werribee Treatment Plant Ammonia Levels Drop 78%
The Western Treatment Plant in Werribee is one of Victoria’s most significant pieces of environmental infrastructure.
Spanning 10,500 hectares — about the size of Phillip Island — the Melbourne Water-managed site sits 30 kilometres west of Melbourne’s CBD and brings together sewage treatment, working agricultural land and internationally recognised wetlands.
One of the clearest improvements was recorded offshore from the Treatment Plant, where ammonia levels have fallen 78% since 1990. EPA attributes the decline to engineering improvements and stronger controls.
Melbourne Water’s Executive General Manager of Service Delivery, Sue Jackman, welcomed the results.
“The improved ammonia levels highlight the impact of sustained upgrades, improved technology and smarter processes at the Western Treatment Plant,”
“We’ll continue modernising the plant so the bay remains heathy, resilient and safe for the community and for the precious environment the bay sustains.” she said.
For the scientists on the water, each trip adds another layer to a record stretching back to 1985.
Once the boat returns to shore, some of the collected water is filtered on a portable lab table that folds out from the back of a ute. Another portion is frozen for later testing.
Those samples and readings will be added to decades of existing data, helping scientists track how Victoria’s coastal waters are changing — and whether efforts to protect them are working.
