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

Sydney’s popular Manly Beach and other beaches around the Australian city were closed on Tuesday as authorities investigated marble-sized balls of white and gray debris that had washed on shore, in the latest such mysterious incident in recent months.

All but one of the nine major north Sydney beaches which were closed this week after mysterious ball shaped debris washed up on the sands have now reopened.

Workers have cleaned up and reopened seven of nine northern Sydney beaches after mysterious balls washed ashore.

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.

But repeated occasions where wastewater is causing pollution and with no clear source must be addressed by the pollution watchdog and Sydney's water authority, Greens environment spokeswoman Sue Higginson said.

Sydney’s popular beaches, including Manly, were closed after marble-sized white and grey balls of debris were discovered washing ashore. This marks the latest mysterious incident in a series of similar occurrences in recent months.

The Northern Beaches Council said that efforts were underway to safely remove the debris. Meanwhile, Local authorities collaborated with the state’s environmental agency to investigate the matter.

Nine beaches in Sydney were shut down for visitors on Tuesday after mysterious white and grey marble-sized balls washed up ashore, disrupting the summer holiday season.

The discovery of the marble-sized balls comes after a similar incident in October closed Sydney's Bondi Beach, among other tourist hotspots.

Mysterious balls appear on Sydney beachesNorthern Beaches Council