Fatberg near Malabar likely produced debris balls that closed Sydney beaches

A secret report identifies an accumulation of fats, oils and grease in an inaccessible chamber of the Malabar deepwater outfall as the likely origin of debris balls that washed up on Sydney beaches in late 2024 and early 2025.

A secret assessment for the New South Wales Environment Protection Authority identifies a large build-up of fats, oils and grease (FOG) in an inaccessible chamber of the Malabar deepwater ocean outfall. The document links that accumulation as the working hypothesis for the debris balls that washed ashore in October 2024 and January 2025. The chamber sits beyond bulkhead stopboards and cannot be safely accessed without taking the outfall offline. Authorities and Sydney Water are reviewing options while undertaking partial cleanups and regulatory work. Key findings: - The Doof assessment (dated 30 August 2025) states FOG likely accumulated in a quiescent zone between the Malabar bulkhead door and the decline tunnel, and that sloughing events could have released debris balls. - The report estimates the accumulation could be large (described as potentially the size of four buses) and notes a 300-cubic-metre chamber beyond the stopboards where material could collect; exact size is uncertain because the area is inaccessible. - The first debris landing at Coogee on 15 October 2024 followed a four-minute loss of raw sewage pumping; a similar rapid drop and rise in flow during wet weather on 11 January 2025 is cited as another likely triggering event. - Sydney Water removed 53 tonnes of accessible FOG in April 2025 but says the chamber beyond the stopboards cannot be safely entered without taking the outfall offline and diverting effluent to a cliff-face discharge, an approach described in the report as unprecedented and likely to close beaches for months. - The report records long-term increases in contaminants: FOG concentrations up about 39% over 10 years and volatile organic compounds up about 125%, and notes Sydney’s system performs primary treatment rather than secondary treatment used in some other cities. - The EPA is working with Sydney Water on a removal program and is considering licence variations to address the build-up; the state has announced a Malabar system investment program estimated at $3 billion over the next ten years. Summary: The assessment presents accumulated FOG in an inaccessible Malabar chamber as the likely source of the debris balls that reached Sydney beaches. Fully accessing and removing the material would require taking the deepwater outfall offline and diverting effluent, a step that the report says could close beaches for months, so authorities are pursuing partial cleanups, regulatory review and longer-term investment and remediation planning. Licence variations are expected to be finalised in the coming weeks and further operational work is underway.