Tests conducted by Randwick City Council discovered the debris is actually a phenomena known as "tar balls".
The mystery surrounding the ball-shaped debris washing ashore in Sydney has been solved after a second beach was closed over the strange objects.
Tests conducted by Randwick City Council have discovered the debris is actually a phenomenon known as "tar balls", the council announced late this afternoon.
The council said the washed-up balls were "consistent with the makeup of tar balls".
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A tar ball is a small blob of oil that has been weathered and shaped after floating in the ocean for a period of time.
Randwick Mayor Dylan Parker said council staff were working fast to remove the balls from the beaches.
"Our community is rightfully very protective of our natural environment and this has been a very concerning incident," Parker said.
"Our priority as a local council is to keep people safe and protect as far as possible our coastal and marine environment."
Parker said the clean-up process would likely continue into tomorrow.
The origin of the tar balls remains unknown, however, the council said it would work with authorities to pinpoint it.
Coogee Beach was closed yesterday afternoon after the balls washed up, with clean-up crews seen at the beach today.
The next beach along the coast, Gordons Bay, was also closed today as the small black spheres were spotted on the sand.
The tar balls were also found scattered along the length of the shore this afternoon by lifeguards.
"We're currently investigating exactly what the source of this mysterious beach pollution is," Parker said at the time.
Randwick City Council collected samples to investigate their materials and origin.
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The beach remains closed.
"We thought we'd have a swim, walk along the beach, and lo and behold, we can't even get on the sand," one would-be beachgoer told 9News.
The matter has been reported to the Environmental Protection Authority and Beachwatch NSW.