The New South Wales environment watchdog has ordered Sydney Water to remove fats from its Malabar wastewater treatment plant, a month after Guardian Australia revealed a huge fatberg was responsible for the poo balls that closed beaches last summer.
Sydney Water isn’t sure exactly how big the fatberg is because it cannot easily access the area where it has accumulated. It could be the size of four Sydney buses.
Fixing the problem would require shutting down the ocean outfall – which reaches 2.3km offshore – for maintenance and diverting sewage to “cliff face discharge”, which would close Sydney’s beaches “for months”, a secret report obtained by Guardian Australia using freedom of information laws states.
This has “never been done” and is “no longer considered an acceptable approach”, the Sydney Water report from August 2025 acknowledges.
The Environment Protection Authority (EPA) said on Monday it had issued a pollution reduction program to Sydney Water, “requiring a range of significant works, including fat removal from the Malabar deep ocean outfall bulkhead area, to reduce the likelihood of further debris balls washing up on the state’s beaches”.
“The requirements on Sydney Water include a range of short, medium and long-term actions including removing the build-up of fats, oils and grease (FOG) from a hard to access bulkhead area of the deep ocean outfall,” the watchdog said in a statement.
Sydney Water was already cleaning that hard to access area, itself “an extremely risky operation”, Guardian Australia reported in January.
The water authority in April 2025 removed 53 tonnes of accumulated FOG, including debris balls, the August report states.
The EPA has now told Sydney Water it must carry out at least 18 inspections of the area over three years from April 2026.
The secret Sydney Water report reveals “the working hypothesis is FOG accumulation in an inaccessible dead zone between the Malabar bulkhead door and the decline tunnel has potentially led to sloughing events, releasing debris balls”.
The bulkhead door is usually under water, and can only be opened at low tide and during low flows in the system. The report states it is impossible to safely go beyond the stopboards. The huge fatberg is thought to be in a 300 cubic metre chamber beyond the stopboards.
Sydney Water won’t shut off the ocean outfall to access the fatberg in the “inaccessible” zone. But Guardian Australia understands the corporation is using remote equipment – and assessing additional methods – to inspect and attempt to remove the blockage.
Sydney Water was further ordered to develop “a system to capture debris overflowing from the sewer during severe wet weather events”; conduct “a study into the formation and weathering of debris balls to make it easier to track them”; and consider “AI or other technology to monitor for the formation of debris balls”.
The corporation has until the end of the year to design the system to capture wet weather overflow at the Mill Stream emergency relief structure. The investigations at Malabar must consider “the use of closed circuit TV, artificial intelligence and computational fluid dynamics to remotely monitor for the formation of debris balls within the plant”.
The NSW EPA executive director of operations, Steve Beaman, said Sydney Water was “responsible for ensuring it doesn’t pollute our beautiful beaches and this important work is a step towards that”.
“Debris balls are a complex problem and the EPA will continue to regulate Sydney Water to protect our precious natural environment.”
A Sydney Water spokesperson said the agency would “implement these measures in close collaboration with the EPA”.
They said the initiatives aligned with its own $3bn Malabar system investment program, which involves infrastructure upgrades to support Sydney’s growing population while reducing discharges at its three ocean outfalls at Bondi, North Head and Malabar.
The debris balls first closed beaches in October 2024. A month later, Sydney Water acknowledged the balls “may have absorbed wastewater discharge, which was already present in the water while forming”, but insisted “they did not form as a result of our wastewater discharges”.
Subsequent reporting by Guardian Australia revealed this statement was not true.
Earlier this month, Sydney Water’s managing director, Darren Cleary, admitted as much, telling the ABC: “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.”
The August report states the first poo balls to wash up on Coogee beach on 15 October 2024 were likely caused by a loss of power at the Malabar plant, which stopped “raw sewage pumping” for four minutes. The subsequent “rapid increase to high flow again” could have dislodged part of the fatberg accumulated behind the bulkhead door.
A similar drop and then increase in pressure, this time “due to wet weather”, occurred on 11 January 2025.
“This rapid change in instantaneous flow could also have given rise to the debris ball landings in January 2025,” the report states.
