Hundreds of tar balls have surfaced on Sydney beaches. But what are they?

It would seem Bondi was open like any other day, despite being closed due to the unknown origins of these Tarballs. “The concerns however didn't deter these beachgoers from taking a swim or catching some rays.” "Did you know the beach was closed today? No. "Did you know the beach was closed today? No I didn't. "Oh really? No." ABC news can reveal the same spherical balls found at Coogee on Tuesday afternoon, are now being seen here as far south as botany bay. In all tarballs have washed up at 11 beaches. "Will be managing the response for this incident out of our head office at Roselle. We'll be opening up our state maritime incident Coordination Center." A blockade and tape wasn't enough to stop swimmers at Clovelly today. "What doesn't kill you makes you stronger" "Apparently seawater is better for a tan" "Not too concerned about what might be in the water?" "No, I don’t think so. it is spread all over the place. nah there is none in there, well none that I can see" But some were more cautious than others. "No, we didn't want to go against the rules, so we didn't go in, but we really wanted to" "We will have to try and find somewhere else, because when you have children they love the water, yeah so you want to go somewhere where the children can swim so very disappointed" Initial test results revealed the spheres are petroleum-based they're created when oil mixes with water and debris. "It is possible we might not find out the cause" One possible source could be a New Zealand navy vessel which sank off the coast of Samoa. Something NSW maritime says is highly unlikely but not off the cards. "We will be able to do the reverse drift modelling taking into account the winds and currents over a number of days." For now, the clean-up continues.