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Examining the mysterious debris spheres that recently necessitated the closure of beaches in Sydney and along the south coast, authorities have concluded that they most likely originate from Sydney Water’s land-based sewage treatment infrastructure, as stated by the New South Wales Environment Protection Authority (EPA).

This conclusion comes after an exhaustive scientific and technical investigation that discovered parallels between the content of the debris spheres and samples collected from several major wastewater treatment facilities operated by Sydney Water, including those at Malabar and Bondi, according to an EPA statement released on Friday.

Professor Stuart Khan, the head of civil engineering at the University of Sydney and who chairs a wastewater expert panel offering scientific advice to the EPA and other NSW government agencies, noted that many aspects of the situation remain unclear.

Khan highlighted the difficulty in determining the contamination source within the sewage network. The contamination could stem from various points in the system, such as before or after the treatment plants, or from the sewers themselves. Also, it is uncertain if the issue is linked to overflow events during wet weather, contamination originating upstream, or discharges from the deep ocean outfall.

A major question^{1} is why these incidents have surfaced now, considering the waste appeared along some of Sydney’s most popular beaches during the peak tourist season. Understanding the root cause is essential for addressing the issue.

Investigations have been ongoing since Guardian Australia first reported in October 2024 that scientists were exploring whether the debris could be tied to sewage. A notable moment occurred in November when the EPA revealed the content, albeit not the source, of the beach debris on the day of the US election. Sydney Water maintained at the time that there had been no operational issues with the Bondi or Malabar wastewater treatment plants.

In January 2025, it was reported that Sydney’s unique sewerage system was likely responsible for the fecal and fat balls found on beaches. This was followed by the revelation in February that a $32 billion project aimed at improving the sewerage system over the next 15 years would not eliminate the practice of discharging waste into the ocean, particularly off the city’s famous eastern suburbs beaches.

The EPA’s Director of Operations, Adam Gilligan, expressed that the EPA’s findings represent significant progress in the investigation, yet emphasized that further work is necessary. He affirmed that the composition of the debris aligns with a land-based sewage origin, even though the exact cause of the pollution remains undetermined.

The EPA dispatched an investigation notice to Sydney Water, compelling the company to conduct oceanographic modeling to assess the spread of the debris; undertake a sampling and analysis program at its sewage treatment plants; and evaluate its deep ocean outfalls and sewerage network to pinpoint the origin of the debris within its systems to prevent future occurrences.

Sydney Water has implemented an internal review. As stated by Sydney Water’s acting executive general manager of water and environment services, Louise Beer, all coastal treatment facilities are functioning normally, and the company is adhering to regulatory standards. Despite finding no faults within its system, Sydney Water proceeded with comprehensive sampling and analysis of the debris at its laboratories and hired an independent oceanographer to ascertain the geographic origin of the debris.

The investigation suggested that the spheres may have formed due to an accumulation of fats, oils, and greases in the wastewater system over time, exacerbated by unique oceanographic factors and weather conditions leading to their appearance on beaches this summer. Sydney Water urges residents to refrain from disposing of fats, oils, and greases in drains.

Dr. Jon Beves, a chemistry professor at UNSW who led the analysis of balls discovered on Coogee beach and Sydney’s north shore, whose

Source: https://www.theguardian.com/australia-news/2025/apr/04/sydney-sewage-treatment-plants-debris-balls-epa-investigation