Authorities reveal cause of mystery debris balls which washed up on Sydney beaches in gross phenomenon

Environmental authorities have revealed the cause of mysterious, sticky and stinking grease balls which washed up on Sydney beaches in gross scenes - narrowing them down to one of the city’s own wastewater treatment systems. The tar-like balls floated onto Sydney beaches between October 2024 and February 2025 and investigations now suggest the fatbergs have reformed inside the tunnel which spits out filtered water into the sea, kilometres offshore. In a statement posted on Friday, the NSW Environment Protection Authority (EPA) says the Malabar Wastewater Treatment System is the likely source. The Malabar system runs across 30km of Sydney, starting in the western suburbs. Authorities say this network is the likely cause because the other wastewater systems pick up less of the industrial waste found in the ball-shaped debris. The EPA says by the end of the year, its investigation will help Sydney Water create “strategies to reduce the likelihood of a similar incident from recurring”. In a statement, NSW Water Minister Rose Jackson pointed to the schedule of hundreds of millions of dollars in maintenance and upgrades planned over the coming decades. “Sydney Water is now working to prevent future events through new programs to help reduce the amount of fats, oils and grease entering the wastewater system,” she said. “They also have a long-term plan to ensure the sewage system can meet the needs of a growing city and a changing environment.” The globules closed beaches at Bondi, Bronte, Dee Why, Freshwater, Long Reef, Manly, Maroubra, North and South Curl Curl, North Steyne and North Narrabeen, Queenscliff and Tamarama at various stages beginning in October 2024, until the end of summer four months later. The first floaters arrived at Coogee, and within weeks scientists were saying the balls contained more human waste than industrial runoffs as expected. Testing uncovered hundreds of different components, including molecules from cooking oil and soap scum, faeces, PFAS chemicals, steroidal compounds, antihypertensive medications, pesticides and veterinary drugs. The fats, oils and high calcium levels suggested the blobs were “fatbergs”, which are commonly formed in sewage systems. Fatbergs are clumps of fat, oil and grease, which cooler water binds together with debris like wet wipes. About 20,000 fatbergs each year cost Sydney Water $27m to clear. The Malabar treatment system removes solids from the wastewater, but not the fats, oils and grease; which can be done using bacteria. The filters on the Malabar system should catch fatbergs, so the EPA now thinks the balls are reforming inside the pipe which deposits wastewater 3.6km out to sea. A 2020 CSIRO report found the sprawling Malabar catchment and system discharged between 5.4bn to 120bn microplastic particles into the ocean each day. The Cronulla system, using better treatment systems, discharged 86m to 350m particles each day. The offshore Malabar pipe expels the treated effluent 3.6km offshore, and ends at 82 metres below sea level. Eighty per cent of Sydney’s sewage was expelled at the shoreline until 1990, when three deepwater ocean pipes were installed. Bacterial contamination along 32km of Sydney’s coastline fell between 26-99 per cent in the first few years after the pipes were installed. Along with Malabar, the North Head and Bondi wastewater systems diffuse the effluent out in the ocean at ratios between 100:1 and 1000:1.