Bondi Beach has reopened for swimmers after around 2,000 black balls washed ashore in Sydney this week.
The tar-like spheres started appearing on Tuesday and multiple beaches were shut due to fears they could be highly toxic.
Workers in orange boiler suits and face masks have been collecting the balls over the last few days.
They were initially believed to be tar balls, formed when oil comes into contact with debris and water, often as a result of oil spills or seepage.
Authorities said this weekend tests were ongoing and the source remained "somewhat of a mystery" - but they now know what's in them.
"Based on advice from the Environment Protection Authority, 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," said New South Wales maritime boss Mark Hutchings.
He said they were still washing up on Friday but in fewer numbers.
The balls are not believed to be harmful when left on the sand but the public are still advised not to touch them.
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The spillage had forced councils to close beaches including Bondi, Bronte, Maroubra, Clovelly, Tamarama, Gordon's Bay and Coogee as a precaution.
Sydney is renowned for its beaches and has more than 100 in its harbour and along the oceanfront.
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