Months after mysterious black balls forced the closure of some of Sydney's most famous beaches, small marble-like debris has begun washing up on the city's shores again. The balls - this time grey or white in colour - have prompted councils to shut nine beaches, including popular Manly and Dee Why, while authorities investigate.

Sydney’s iconic beaches are famous worldwide for their golden sand and pristine waters. They attract millions of tourists every year, but this time, they have drawn the attention of researchers and local authorities for an unusual reason.

Nine beaches in Sydney, including the well-known Manly beach, were closed to swimmers on Tuesday after small white and grey balls of debris washed up on the shores.

On Tuesday, January 14, nine beaches in Sydney were closed to swimmers due to mysterious balls washing ashore. Local authorities are already working to determine the origin of these findings. Sydney's ocean beaches,

UNSW School of Chemistry Professor Dr Jon Beves says testing will commence to investigate what the mystery balls shutting down Sydney’s beaches are composed of.