In a precautionary move, authorities have closed nine beaches along Sydney's northern coastline after the mysterious appearance of grey, ball-shaped debris.

Spanning a 13-kilometer stretch, this incident has prompted swimmers and surfers to vacate coastal areas such as Manly, Collaroy, and North Narrabeen.

These recent events follow a similar scenario that transpired three months prior, when 2,000 black tar balls, identified as a mixture of human hair and household fats, were discovered across Sydney's eastern beaches.

While investigations are ongoing, water scientist Ian Wright notes that the method of occurrence is very similar to previous incidents, suggesting possible origins in sewerage.

"It may not be the case that the source is sewerage," said Wright, "but it needs to be treated with appropriate caution." The Northern Beaches Council echoed these concerns, stating that most of the debris is marble-sized, although some pieces are larger.

Authorities were alerted by state environment officials and have begun prompt testing and safe removal of the material.

Despite a recent spell of heavy rain in the region, Sydney Water assured the public that wastewater treatment facilities are functioning within normal parameters, serving approximately 1.1 million residents.

A spokeswoman for the company affirmed compliance with licences set by the NSW Environment Protection Authority (EPA), emphasizing the ongoing collaboration with the EPA to ascertain the cause of the incident.

Local political figures have weighed in on the issue, urging greater accountability and transparency.

Sue Higginson, the Greens environment spokeswoman, flagged recurrent wastewater-related pollution as an alarming trend.

She stressed the necessity for Sydney Water and the pollution watchdog to engage in "a serious conversation about the accountability of utilities."

The NSW EPA remains in communication with relevant authorities, seeking clarity on these unsettling occurrences affecting the city's renowned beaches.