More sewage debris balls have washed up on Sydney beaches near a waste treatment facility after a weekend of heavy rain.
The Malabar Wastewater Treatment System was identified as the likely source of the mysterious balls that turned up at beaches across Sydney, the South Coast and the Central Coast in late 2024 and early 2025.
But more were found on Malabar Beach in Malabar and Foreshore Beach in Botany Bay on Monday.
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Sydney Water has erected signs urging beachgoers not to touch any sewage debris balls as it investigates the cause.
"The exact origin and cause is under investigation," a Sydney Water spokesperson said.
"Sydney Water crews have been on site over multiple days, leading both coordination and on-beach clean-ups, supported by council, while undertaking visual inspections, collecting and removing observed debris balls, and disposing of all material in accordance with environmental and safety requirements."
The balls have washed up after heavy rainfall and flash flooding in Sydney, which saw up to 140mm of rainfall within hours.
Authorities believe the weather could be to blame for why four people were attacked by sharks within 48 hours in NSW.
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The sewage debris balls are made up of an increased load of grease, fats and oils that have built up in the state's wastewater system over time.
Sydney Water said Malabar's deep ocean outfall likely caused these balls at coastal beaches, while the Mill Stream emergency release structure is responsible for those at beaches in Botany Bay.
The state has thrown $3 billion at upgrading the Malabar Wastewater Treatment System over 10 years to prevent these fatty and greasy sewage balls from washing up on the coastline and accommodate more customers.
"We understand the seriousness of recent debris ball incidents and the need to ensure our network is equipped for Sydney's growing population," Sydney Water chief executive Darren Cleary said when the funding was announced last week.
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