Testing has revealed that hundreds of materials from household fats to human hair made up the thousands of mysterious black balls that washed up on some of Sydney's most popular beaches.
But where they came from remains a mystery.
Fatty acids from cooking oils, soap and skincare products, as well as petroleum hydrocarbons, were found alongside hair, food waste and other naturally decomposing substances in the balls.
They likely came from a source of "mixed waste" involving hundreds or even thousands of different materials, the NSW Environment Protection Authority said in a statement late on Wednesday.
"However, due to the complex composition of the balls and the time they have spent in the water, testing has not been able to confirm their exact origin," the agency added.
"Authorities have so far been unable to trace the source, but final results are due in the coming weeks."
Several beaches in Sydney's eastern suburbs were closed in October after the balls were first found washed up at Coogee.
About 2000 were picked up in an emergency clean-up operation.
Testing of the balls was conducted by the environment department along with University of NSW scientists.
Sydney Water confirmed it had found no issues with the operation or with maintenance on wastewater facilities near the beaches at the time.
Analysis of weather patterns in the lead-up also revealed no conclusive information.
The washed-up waste was originally thought to be "tar balls", which form when oil comes into contact with debris in water.
That would suggest a spill or seepage from a ship as the source of the pollution, but the testing showed similarities to "fatbergs" that can form in and clog sewerage with household waste.
Sand, calcium salt and bacteria commonly associated with wastewater were also identified during analysis of the balls.
