Likely source for Sydney's debris balls found

The NSW Environment Protection Authority’s (EPA) investigation into the source of debris balls on Sydney and South Coast beaches over recent months has determined they likely originated from Sydney Water’s land-based sewage treatment network.

The development comes after a comprehensive scientific and technical investigation found similarities between the make-up of the debris balls and samples taken from several of Sydney Water’s major wastewater treatment plants, including those at Malabar and Bondi.

Since October 2024, when the debris balls first appeared on Eastern Suburbs beaches, the EPA has completed extensive chemical analysis of the balls. In November and December last year, it shared test results identifying that the debris contained fatty acids and petroleum hydrocarbons, as well as organic and inorganic materials.

The EPA’s investigation into the origin of the debris balls was expanded earlier this year after additional pollution events on the South Coast and Northern Beaches. Debris balls were sampled at beaches around Sydney and two South Coast beaches from October 2024 to January 2025. Several of Sydney’s wastewater treatment plants and visiting cruise ships were sampled for comparison.

EPA Director Operations Adam Gilligan said the EPA has now issued an investigation notice to Sydney Water in an effort to pinpoint the precise source or sources of the debris balls within the Sydney Water network.

“This is a significant step forward in our investigation but there is still work to do,” Gilligan said.

“While we are yet to determine exactly what caused the pollution incidents to occur when they did, we can say the composition and the characteristics of the debris balls are consistent with a land-based sewage source.

“The community has been eager for answers and to assist in our ongoing investigation we’ve established a Wastewater Expert Panel to provide independent scientific advice to the EPA and other NSW Government agencies.

“We are pleased to announce Professor Stuart Khan, Head of School of Civil Engineering at The University of Sydney, has agreed to chair the panel and we’ll confirm details of the panel membership soon.”

The EPA’s Investigation Notice will require Sydney Water to:

• undertake oceanographic modelling of the dispersion of the debris balls;
• complete a sampling and analysis program at its sewage treatment plants; and
• assess its deep ocean outfall systems and its sewerage pipe network to identify where in its systems the debris balls originated to prevent a recurrence.
   

The community is reminded to avoid touching debris balls or any pollution on their beaches and to immediately report new finds to their local council or the EPA’s Environment Line on 131 555.

Image caption: Black, ball-shaped debris washed up on Coogee Beach in October 2024. Image courtesy Randwick City Council.