A marine expert has revealed the likely source of the hundreds of mysterious black balls that have washed up on Sydneys Coogee Beach - and warned they could be carcinogenic.
The popular beach in Sydneys eastern suburbs was immediately shut down after lifeguards came across the worrying discovery on Tuesday.
It looks like tar balls or oil balls, marine biologist Lawrence Chlebeck told Daily Mail Australia on Wednesday.
This is what happens when theres an oil slick or a release of oil. It could be from manmade sources, it also could be from natural sources, he said.
Mr Chlebeck said such balls form in a similar way to how pearls form in oysters.
These things are out in the water for a long time, they coagulate around a small piece of debris, whether thats a piece of plastic or a stick or something and they kind of coalesce around one of these things, he said.
And then through either storms or currents, they can wash ashore so it could have been travelling for quite a while and could come from a long way away.
The marine biologist said it was rare for such balls to wash up on Australian shores and that it is more commonly witnessed in the United Sates.
A marine expert has revealed the likely source of the hundreds of mysterious black balls that have washed up on Sydneys popular Coogee Beach (pictured)
Randwick Council workers are pictured cleaning up Coogee Beach in Sydneys east
In different parts of the world where there is a lot of oil and gas exploration right off the shore, say like the Gulf of Mexico, these things are found on beaches in Texas and Louisiana quite frequently, he said.
If certain oil and gas exploration projects go through off the coast of Sydney, as they have been discussed in the not too distant past, we could be seeing more of this kind of thing happening.
Mr Chlebeck warned that the black balls can definitely be carcinogenic.
Coogee Beach was closed for that concern. It can tarnish bird feathers so they cant dry and they drown, he said.
While wildlife mostly know to stay away from the balls, sometimes humans curiosity gets the better of them and they cant resist touching them.
The marine expert advised beach-goers who come into contact with the balls to clean the area with washing-up liquid.
That anti-oil coating substances in washing-up liquid is probably the best thing to get it off, Mr Chlebeck said.
But people should definitely avoid that beach for now and avoid swimming in areas where there might be these tar balls floating around.
Randwick Council mayor Dylan Parker said the balls were being analysed with results to come back within a day or the next two days.
There looks to be an oil spill or slick but its still under investigation. Initial reports seem to suggests some sort of oil pollution or contamination, he said.
Coogee Beach in Sydneys east (pictured) will remain closed until further notice
Randwick Council suspects the material (pictured on Tuesday) may be tar balls
The beach was closed on Tuesday and will remain closed until further notice to preserve community safety, Mr Parker said.
They do resemble tar balls, he said. If it is potentially oil, its not safe to touch or consume. It can be potentially carcinogenic.
Randwick Council is liaising with the NSW Environment Protection Agency, Beach Watch NSW and other relevant bodies on when it is safe to open the beach again.
This has never happened before, the mayor said.
At this stage it is unknown what the material is, however, they may be "tar balls" which are formed when oil comes in to contact with debris and water, typically the result of oil spills or seepage, the council said.
A further update from the council is expected later on Wednesday.
Coogee is one of Sydneys most popular beaches and a tourist hotspot.