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 pumping of primary-treated effluent into the ocean makes us out of step with the rest of the world, a water engineering expert said.

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.