Hundreds of mysterious black tar-like balls have washed up on two popular Sydney beaches, prompting lifeguards to close the strands to swimmers. “Mysterious, black, ball-shaped debris” began appearing on Coogee Beach on Tuesday afternoon the local mayor said, leaving flummoxed Australian authorities scrambling to find out what they might be, and where they may have come from. Hundreds of golf-to-cricket-ball-sized spheres could be seen littering the coast, which is usually thronged with Sydneysiders and tourists.

Instead, a few seagulls wandered among the spheres, pecking and examining. The balls were also spotted at nearby Gordon’s Bay, an aquatic reserve popular for snorkeling and fishing, which was also closed. “At this stage, it is unknown what the material is,” Mayor Dylan Parker said in a social media post. “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.”—AFP