A confidential scientific report has identified the deepwater ocean outfall at Malabar as the likely source of the fatberg balls that forced the closure of several Sydney beaches last summer. The report, obtained by Guardian Australia under freedom of information laws, points to a combination of heavy rainfall and a buildup of fats, oils and greases (FOGs) in the sewerage system as the cause of the debris.
The New South Wales Environment Protection Authority (EPA) confirmed on Friday that evidence collected by Sydney Water had narrowed the origin of the debris to within the Malabar system. The EPA stated that Sydney Water's Malabar wastewater treatment system was the likely source of the debris balls that washed up on NSW beaches between October 2024 and February 2025.
The oceanographic modelling report by WQ Data notes that FOGs in the sewerage system provide the 'stickiness' for the debris balls, allowing particulate material to adhere. High rainfall in the year leading up to the discharge 'primed' the system, and further rainfall within a few days before the release was sufficient to move the combined FOGs and particles out of the pipes. Wave action then rolled the material into balls.
Authorities remain unable to predict when the balls might wash up again but are urgently working on solutions. Sydney Water's environment manager, Ben Armstrong, said fat was accumulating somewhere in the system, but its exact location was unknown. The EPA's independent expert panel has recommended further investigations to pinpoint potential sources within the Malabar system.
Professor Stuart Khan, chair of the EPA's advisory panel, noted that the Malabar sewer has had a long time for FOGs to build up, serving nearly two million customers. He cited population growth and an increase in food outlets as contributing factors. The EPA previously stated that testing confirmed the balls were consistent with human-generated waste such as grease and faecal matter.
