Sewage Practices Under Fire After Dee Why Grime Balls Mystery

Dee Why Grime Balls

The recent appearance of marble-sized grime balls on Dee Why Beach has raised concerns over Sydney’s sewage system, with experts linking the pollution to outdated wastewater management.



Background: Grime Balls and Beach Closures

Dee Why Beach was among nine Northern Beaches Suburbs temporarily closed in January 2025 after white and grey grime balls washed ashore. The phenomenon follows similar incidents over the past six months, including discovering black grime balls on beaches from Bondi to Coogee in late 2024. The balls, which range from pea to marble size, have been found to contain fats, oils, human hair, and traces of medications, strongly indicating a link to sewage pollution.

The NSW Environment Protection Authority (EPA) and Sydney Water are investigating the origin of the debris, but no conclusive answers have been found. Experts have suggested that Sydney’s wastewater system, which relies on primary treatment, could be the source of the recurring pollution.

Dee Why Grime Balls
Photo Credit: 顶真新闻/Facebook

Sydney’s Sewage System in Focus

Sydney’s primary treatment plants at North Head, Malabar, and Bondi only remove solids and skim fats and grease from wastewater before discharging the effluent into the ocean via deepwater outfalls. These pipes, built in the 1990s, extend 2 to 4 kilometres offshore but do not address dissolved contaminants, oils, or smaller particles in the water.

Stuart Khan, a water treatment expert from the University of Sydney, believes the grime balls could form when untreated fats and oils discharged from outfall pipes mix with seawater. Heavy rainfall, like Sydney’s recent summer storms, may worsen the issue by causing leaks or overflows from stormwater systems, which can carry untreated sewage into the ocean.

The Role of Environmental Factors

Experts say ocean currents may distribute the balls across Sydney’s beaches, including Dee Why. The EPA’s chemical analysis of previous incidents found petroleum hydrocarbons linked to shipping fuels, but human-generated waste was confirmed as the primary component. The presence of materials such as hair, calcium, and pharmaceuticals strongly implicates Sydney’s wastewater system.

CSIRO scientist Dr Sharon Hook said the balls appear to form when fats, oils, and non-water-soluble materials combine in the ocean. She warned that while the exact source remains unknown, the balls clearly pose environmental and public health risks, advising beachgoers to avoid touching them.

Historical Context and Calls for Change

Sydney’s reliance on primary sewage treatment has been criticised for decades. In the 1980s, the Stop the Ocean Pollution (STOP) campaign advocated for secondary treatment to be added to Sydney’s wastewater plants, which would include biological filtration and finer contaminant removal. However, the city instead opted to extend the outfalls, citing cost concerns.

Environmental advocate Dr Richard Gosden, a member of STOP, said Sydney’s decision to forgo secondary treatment decades ago is now contributing to ocean pollution. He described the situation as a failure to protect both marine ecosystems and the community. Similar sentiments were echoed by Professor Sharon Beder, who has studied Sydney’s sewage engineering history and argues that authorities need to act swiftly to modernise the system.

Investigations and Future Plans


The EPA and Sydney Water are working with external experts to trace the origin of the grime balls. Potential sources under investigation include illegal dumping, sewage outfalls, and stormwater runoff. Sydney Water has announced a $30 billion investment plan to modernise wastewater infrastructure over the next decade, but experts believe more immediate action is needed.



Beachgoers at Dee Why and other affected areas are urged to report any new debris to local authorities and avoid closed beaches. Cleanup efforts are ongoing, with councils working closely with the EPA to manage and dispose of the pollution safely.

Published 21-January-2025

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