The golf-ball-size debris that led to beach closures across the Australian city was not tar balls as first thought, but was instead made up of decomposed cooking oils, hair and food waste.

The mystery of the black balls that washed up on some of Sydney’s most iconic beaches last month has now been solved – and it’s more disgusting than you could ever imagine.

Eight beaches including Bondi were closed for several days and a massive clean-up ordered after thousands of the black deposits started appearing from 16 October. Testing by chemists has determined the balls were most likely the result of a sewage spill,

"I always expected them to be like crude oil, and if you smell kerosene or ... even heavy oil, it doesn't smell that bad," said one researcher. "But this really smells disgusting. It smells much more like what you'd expect in a sewer.

Disgusting’ black balls which washed up on multiple Australian beaches have been identified as an odd concoction of substances. Last month, beaches in Sydney were closed as authorities looked into the bizarre black balls which washed onshore.

A mystery that baffled Sydney beachgoers has been solved, with the makeup of the balls that washed up on NSW shores revealed to be human-made waste.