A massive fatberg, potentially the size of four buses, is blocking a critical sewer tunnel in Sydney, and authorities admit it may be inaccessible for removal, contributing to the ongoing issue of foul-smelling debris balls washing up on the city’s beaches.
Sydney Water managing director Darren Cleary acknowledged the difficulty of addressing the blockage, located within a tunnel at the Malabar Water Resource Recovery Facility in Sydney’s east. “We don’t know exactly how big the fatberg is,” Cleary told 7.30. “The size of four buses, that would be the maximum potential extent of it. It may be that, it may be slightly smaller. We don’t exactly know.”
A technical report released by Sydney Water details a significant build-up of fats, oils, and greases (FOG) within the tunnels beneath the Malabar wastewater treatment plant. The report illustrates a “plausible hypothesis” suggesting the blockage of an outfall tunnel by FOG is directly linked to the formation of the debris balls.
The bulk of the fatberg resides in a section of the tunnel that is currently unsafe to access, according to Cleary. Still, 53 tonnes of similar material were removed from the facility during wet weather in April of last year.
The report indicates that the debris balls are forming within the sewer network and being released into the ocean approximately three kilometers from the Malabar plant. Flows through the tunnels appear to be skimming the fatberg, creating the balls, which are then smoothed by ocean currents.
Last month, Malabar Beach was temporarily closed due to the continued presence of the debris. Similar closures occurred in late 2024 and early 2025, with tens of thousands of balls washing ashore along a stretch of coastline from the Central Coast to the South Coast.
“I can’t guarantee there won’t be debris balls in the future. We are doing what we can to minimise the risk of that occurring,” Cleary stated, adding an apology for the inconvenience caused to the public.
Cleary also addressed previous statements made by Sydney Water regarding the source of the debris, admitting that earlier assertions denying a link to wastewater discharges were inaccurate. “I think in hindsight, looking back, clearly the evidence is saying it most likely was the ocean outfall. So with the benefit of hindsight, yes, those earlier statements have been shown to be not factually correct.” He explained that initial assessments indicated the outfalls were functioning as designed, and the unexpected appearance of the debris balls was a surprise.
Initial speculation about the composition of the balls, including theories of oil spills or discharges from ships, was disproven by testing conducted by the University of New South Wales (UNSW). Chemistry professor Jon Beves found the balls contained common household waste materials, including soap scum, cooking oils, and faecal matter, as well as traces of pharmaceuticals like recreational drugs and heart medication. “Biomarkers of human waste,” Professor Beves said, describing the contents as “things you’d find at a domestic sewer.”
The formation of fatbergs is attributed to the improper disposal of materials like wet wipes, paper towels, cotton buds, and cooking oils down drains. Sydney Water’s public awareness campaign emphasizes that only water, detergent, and soap should be flushed down sinks.
However, the report reveals a 39 percent increase in the volume of fats, oils, and greases entering the Malabar plant over the past decade.
The Malabar plant serves nearly 2 million residents in Western Sydney and parts of the eastern suburbs. Randwick City Council incurred a cost of half a million dollars to clean up debris from beaches like Coogee during the 2024-2025 incidents, a bill Sydney Water has agreed to cover. Randwick Mayor Dylan Parker indicated a willingness to collaborate on future incidents.
Sydney Water is planning a $3 billion upgrade to the wastewater system, including the Malabar network, to address the issue. The upgrade, which will take 10 years to complete, is intended to prevent the need to take treatment plants offline for maintenance – a step that would require the closure of Sydney beaches for months. Flows into Malabar will be reduced as part of the plan.
