A baffling tar ball emergency that closed major beaches in Sydney’s eastern suburbs appears to be over.

The remaining beaches closed to bathers at Coogee, Maroubra and Clovelly have been cleared to reopen on Saturday after Bondi and several others reopened on Friday.

But the cause of the deluge of black balls that began washing up on Coogee Beach earlier this week, prompting a major clean-up operation, remains unknown.

Mark Hutchings, the executive director of New South Wales Maritime, said that based on health advice, the substance was not highly toxic to humans.

“We can now confirm the balls are made up of fatty acids, chemicals consistent with those found in cleaning and cosmetic products, mixed with some fuel oil,” he said in a statement.

“They are not harmful when on the ground, but should not be touched or picked up.”

Beachgoers have been told to let lifeguards know if they see any tar balls, and if they touch them to clean their hands with soap and water or baby oil.

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About 2,000 balls have been picked up since Tuesday, when the emergency began.

“We’ve found no further evidence of the substance, so this appears to be an isolated incident,” Hutching said.

The NSW Environment Protection Authority is still examining the balls and conducting tests.

“Until we finalise all our test results, we are unable to clearly state where they came from,” said Stephen Beaman, the authority’s executive director.

“It is still somewhat of a mystery and may take a few more days to determine origin.”

On Friday, the NSW government vowed to throw the book at anyone found responsible for the balls.

“We’re investigating to try and find the source of the spill and who is responsible,” the environment minister, Penny Sharpe, said.

Tar balls are formed when oil comes into contact with other debris and water, usually as a result of oil spills or seepage.

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