An iceberg (or fatberg, the name given to a pile of wet towels, garbage, wastewater and leftover cooking oil) the size of four buses may have created the stink balls that forced Sydney's beaches to close. And these beaches cannot be cleaned.
The confidential report said fats, oils and grease accumulated in an “inaccessible dead zone” at the wastewater treatment facility, then escaped when pressure in the pump room “rapidly increased,” The Guardian wrote.
A giant ice floe, the size of four Sydney buses, located in Sydney's Malabar deep sea sewer has been identified as the source of trash pellets that washed up on Sydney beaches a year ago.
Sydney Water doesn't know exactly how big the fat is because it has difficulty getting to where it accumulates. According to a confidential report by Guardian Australia, fixing the problem will require closing culverts 2.3km offshore for maintenance and discharging wastewater into a “cliff”, resulting in the closure of Sydney beaches “for months”.
The report admits that this “has never been done” and is “no longer considered an acceptable approach”. Sydney Water's Deep Ocean Outflow (DOOF) assessment report, dated 30 August 2025, was prepared for the New South Wales Environment Agency, which is investigating the “trash balls” that caused many beaches to close in late 2024 and early 2025.
“The research hypothesis is that the accumulation of fats, oils and lubricants in the inaccessible dead zone between the Malabar bulkhead door and the drainage tunnel is likely to result in sloughing, releasing debris,” the report concluded.
The report said the first fecal pellets washed ashore on Coogee beach on October 15, 2024, possibly due to a power outage at the facility, which stopped “pumping raw wastewater” for four minutes. A subsequent “rapid return to high flow” may have removed some of the grease that had accumulated behind the door on the bulkhead. A similar pressure drop and then increase, this time “due to wet weather” occurred on January 11, 2025.
Sydney Water initially denied its sewerage system was to blame, saying in November 2024 that there were “no issues with the normal operation of the Bondi or Malabar wastewater treatment works”.
Last November, the Environmental Protection Agency (EPA) admitted – after Guardian Australia reported on separate secret oceanographic modeling – that data “collected by Sydney Water showed debris had entered the Malabar system”. Malabar spillway began operations in 1990.
Unlike most cities, Sydney only carries out primary wastewater treatment – solids removal. In other places, secondary treatment uses settling tanks and disinfection techniques before discharging or treating wastewater.
For example, Singapore treats wastewater at such a high level that it can be reused to provide drinking water, The Guardian writes.
Fatbergs have caused problems in other cities, but in different ways. In London in 2017, a block of ice as heavy as 11 double-decker buses and as long as two football fields was discovered blocking part of London's aging sewer network. It took three weeks to remove the congealed grease, wet wipes and diapers.
New York City spends about $19 million each year to remove wen from sewers and implements a “Throw it out, don't flush” campaign.
