Authorities reveal cause of mystery debris balls which washed up on Sydney beaches in gross phenomenon
Environmental officials have uncovered disgusting scenes narrowing down the cause of a mysterious, sticky and smelly oil pellet washing up on Sydney beaches to one of the city’s own wastewater treatment systems.
Tar-like balls floated off Sydney beaches between October 2024 and February 2025, and research now shows oil mountains have re-formed inside the tunnel, which spews filtered water into the sea kilometers offshore.
In a statement released on Friday, the NSW Environmental Protection Authority (EPA) said the source was the Malabar Wastewater Treatment System.
The Malabar system covers 30 km of Sydney, starting from the western suburbs.
Officials say this network is the likely cause because other wastewater systems are less likely to collect the industrial waste found in the ball-shaped debris.
The EPA says the investigation by the end of the year will help Sydney Water establish “strategies to reduce the likelihood of a similar incident occurring again”.
In her statement, NSW Water Minister Rose Jackson drew attention to the hundreds of millions of dollars of maintenance and improvement plans planned for the coming years.
“Sydney Water is now working to prevent future incidents through new programs to help reduce the amount of solids, liquids and grease entering the wastewater system,” he said.
“They also have a long-term plan to ensure the sewer system can meet the needs of a growing city and changing environment.”
The shovels closed beaches at Bondi, Bronte, Dee Why, Freshwater, Long Reef, Manly, Maroubra, North and South Curl Curl, North Steyne and North Narrabeen, Queenscliff and Tamarama in various stages from October 2024 until the end of summer, four months later.
The first floats arrived at Coogee and within weeks scientists were saying, as expected, that the balls contained more human waste than industrial waste.
Tests revealed hundreds of different components, including molecules from cooking oil and soap scum, feces, PFAS chemicals, steroidal compounds, antihypertensive drugs, pesticides and veterinary drugs.
Fats and oils and high calcium levels suggested that the droplets were “oil bergs” that often formed in sewer systems.
Fatbergs are clumps of fat, oil, and grease that cold water binds together with wipe-like debris.
Cleaning approximately 20,000 fatbergs each year costs Sydney Water $27 million.
The Malabar treatment system removes solids from wastewater but does not remove solids, liquids and grease; can be made using bacteria.
Filters in the Malabar system are supposed to capture the oil bergs, so the EPA now thinks the bergs are reforming inside the pipe that exposes the wastewater 2.2 miles out to sea.
A 2020 CSIRO report found that the sprawling Malabar basin and system discharge 5.4 billion to 120 billion microplastic particles into the ocean every day. Using better purification systems, the Cronulla system discharged between 86 and 350 million particles each day.
The offshore Malabar pipe discharges treated wastewater 3.6 km offshore and ends 82 meters below sea level.
Eighty percent of Sydney’s sewage was discharged from the coastline until 1990, when three deep-water ocean pipes were installed. In the first few years after the pipes were installed, bacterial pollution along Sydney’s 32 kilometers of coastline dropped by between 26 and 99 percent.
In addition to Malabar, the North Head and Bondi wastewater systems distribute wastewater into the ocean at ratios between 100:1 and 1000:1.
