Last month, Sydney’s popular beaches, including Bondi and Coogee, were unexpectedly littered with thousands of foul-smelling black balls, sparking beach closures and prompting investigations into their mysterious origins. Scientists have now solved the mystery, revealing that these black spheres are, in fact, mini “fatbergs” — unpleasant masses composed of human waste, drugs, and grease.

When lifeguards noticed the black balls in mid-October, authorities immediately closed seven beaches and issued warnings to the public, advising them to avoid touching or swimming near the strange formations. Initial tests suggested the balls might be remnants of unrefined oil, potentially pointing to an oil spill. However, further analysis by researchers at the University of New South Wales (UNSW) revealed a far more repulsive composition. According to lead investigator Associate Professor Jon Beves, the fatbergs were made up of human feces, fatty acids, methamphetamine, human hair, and food waste, among other disturbing substances.

“They smell absolutely disgusting,” Beves told Australian media outlet 9News. His colleague, Professor William Alexander Donald, echoed the warning, saying, “I wouldn’t want to be swimming with them.”

Fatbergs, typically found clogging city sewers, form when fats, oils, and grease solidify around debris in wastewater. They’ve been known to reach enormous sizes, like the infamous 330-ton fatberg that blocked a sewer in Birmingham, UK, in 2021. Unlike typical fatbergs, however, these black balls contained a peculiar mix of sewage and chemicals, including recreational drugs and pharmaceutical traces, raising concerns about pollution along Sydney’s coastline.

While the fatbergs’ precise origin remains unclear, experts suspect they might stem from wastewater discharge or a spill from a passing ship. The New South Wales Environment Protection Authority (EPA) has considered various potential causes but has yet to confirm the exact source, given the fatbergs’ complex composition and prolonged exposure to ocean water.

This unusual incident underscores the ongoing challenges of pollution and waste management in coastal areas, as well as the unpredictable impacts of mixed waste on marine environments.