Debris balls found on Sydney beaches in late 2024 and early 2025 have been attributed to a large accumulation of fats, oils, and grease (FOG), referred to as a fatberg, within Sydney Water's Malabar deepwater ocean sewer system. Investigations by Sydney Water and the New South Wales Environment Protection Authority (EPA) identified the Malabar system as the source. In response, the state government has announced a $3 billion investment program over the next decade to upgrade wastewater infrastructure, reduce discharge volumes, and enhance system management.
Discovery and Origin
Debris balls appeared on Sydney beaches, including Coogee, Malabar, and locations in Botany Bay, between late 2024 and early 2025. These appearances extended from the eastern suburbs to the Central Coast. The debris was found to consist of fatty acids, some petroleum hydrocarbons, human hair, and various fibers, with some debris balls containing human faeces. Sydney Water initially denied its sewerage system was responsible but later acknowledged evidence pointed to the Malabar system as the origin.
A large accumulation of FOG, described as a fatberg, within Sydney Water's Malabar deepwater ocean sewer, has been identified as the probable source. The fatberg's exact size is unknown due to its inaccessible location but is estimated to be equivalent to four Sydney buses in scale. It is hypothesized to be located in an inaccessible area between a bulkhead door and a decline tunnel, specifically an intersection chamber estimated at 300 cubic meters. This chamber was not designed for routine maintenance.
A confidential report prepared by Sydney Water for the NSW EPA, dated August 30, 2025, refers to a "working hypothesis" that FOG accumulation in this inaccessible area caused "sloughing events." These sloughing events, where parts of the fatberg detach, are believed to be triggered by rapid changes in pumping pressure.
Timeline of Debris Release
The initial appearance of debris balls on Coogee Beach in October 2024 was linked to a four-minute power loss at the Malabar plant, which disrupted raw sewage pumping. A subsequent rapid increase in flow is believed to have dislodged a portion of the fatberg. A similar event in January 2025, attributed to wet weather, also caused rapid changes in flow, contributing to further debris ball landings. More recently, debris balls appeared on beaches, including Malabar and Foreshore Beach in Botany Bay, following heavy rainfall, with over 100mm falling within hours over a recent weekend.
System Context and Challenges
Sydney Water's Malabar deepwater ocean sewer system serves south-western Sydney, including areas such as Campbelltown, Fairfield, Glenfield, and Liverpool. Sydney's wastewater treatment primarily involves straining out solids (primary treatment). Over the past decade, FOG in the Malabar system has increased by 39%, and volatile organic compounds have risen by 125%.
Addressing the fatberg would necessitate shutting down the Malabar deepwater ocean outfall (DOOF), which extends 2.3 kilometers offshore, for maintenance. This would involve diverting sewage to "cliff face discharge." According to the August 2025 confidential report, this method has not been implemented previously and is no longer considered acceptable, as it would likely lead to Sydney's beaches being closed for an extended period, potentially months.
Foreshore Beach, where debris was found, is frequently rated as highly polluted by Beachwatch due to its proximity to a primary overflow valve for the Malabar sewage system. Sydney Water currently has an agreement to discharge sewage into Mill Stream until July 2027. Similar fatberg issues have been reported globally, including a large fatberg blocking London's sewers in 2017.
Government Response and Future Investment
Minister for Water, Rose Jackson, announced a $3 billion "Malabar system investment program" over the next 10 years. This program aims to upgrade key upstream wastewater treatment facilities and reduce the volume of wastewater treated and discharged via the Malabar deep ocean outfall. The initial phase of the project will focus on upgrading wastewater facilities in Glenfield and Liverpool.
Sydney Water is undertaking both "immediate actions and long-term corrective measures." These include:
- Continued regular cleanups of accessible sections, with 53 tonnes of accumulated FOG and debris balls removed in April 2025.
- Enhancing cleaning and inspection of ocean outfall screens.
- Strengthening trade-waste controls for high-risk customers, as some food businesses reportedly operate without proper waste approvals.
- Expanding public education campaigns to deter FOG disposal down drains.
The NSW EPA is collaborating with Sydney Water to establish a program for FOG removal from the bulkhead area and expects to finalize license variations by mid-February.
Sydney Water Chief Executive Darren Cleary acknowledged the seriousness of the debris incidents and the necessity to prepare the network for Sydney's expanding population. He also stated that Sydney's three deepwater ocean outfalls at Malabar, Bondi, and North Head, which dispose of 80% of the city’s wastewater, have met environmental standards for nearly three decades, and Sydney beaches generally maintain high water quality. He described the debris ball issue as an "unexpected event."
Ms. Jackson noted that temporary appearances of debris balls could still occur but anticipated improvements once pressure on the Malabar system is reduced. Limited disruptions are expected during the project, primarily localized noise and truck movements for residents near construction sites. Sydney Water is also progressing with plans to introduce higher levels of processing at inland plants to produce recycled water, particularly for data centers.