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.

Beaches in Sydney, Australia, were closed to bathers after small white and grey balls of debris washed up on the shores at the height of the summer holiday season.