The sand and acid carbon used in the pools' filtration systems was being replaced, said assistant director of leisure services Paul Cheung Kwok-kee.

The work should be completed by the beginning of next month, including water-quality testing by the Water Supplies Department and Food and Environmental Hygiene Department.

'We have looked at the sand and the acid carbon and have found that there are no worms there,' Mr Cheung said. 'But since we have removed them we have to replace them with new sand and new acid carbons.'

Chinese Olympic divers with gold medals from Athens are expected to perform at the Kowloon Park complex on September 8. The visiting athletes will include Tian Liang and Guo Jingjing, who led China to its first two diving golds of the Games in synchronised diving.

The Kwun Tong swimming pool, also closed after worms were discovered, was expected to reopen within the next three or four days, Mr Cheung said.

There was no need to change the pool's sand and acid carbon filters, he said. The department would increase chlorine levels.

'We have decided to use a thorough and cautious approach in order to allay citizens' concerns,' Mr Cheung said.

A children's pool in Tai Wan Shan, near Hunghom, remains closed indefinitely after worms were found there on Monday.

Mr Cheung said the department would crack down on hygiene standards when the pools reopened.

Staff would be posted at pool entrances to ensure swimmers washed their bodies and feet before entering the water. They would also conduct hourly water-quality tests.

'Citizens should be vigilant themselves to ensure that their bodies are clean, and we also hope that they will keep in mind the sanitary condition of the pools,' Mr Cheung said.

Senior lifeguard representative Alex Kwok Siu-kit said swimmers' cleanliness and sense of responsibility had improved in recent years.

But lifeguards still frequently saw people wearing shoes or slippers into the pool, said Mr Kwok, vice-chairman of the Hong Kong and Kowloon Lifeguards' Union.

Race against time

With the arrival of China's Olympic medallists looming, the Leisure and Cultural Services Department is pulling out all stops to end the bloodworm saga, which began on August 4.

August 4: Department receives first report of bloodworms at Kowloon Park complex and increase chlorine level.

August 12: Second batch of worms is found

August 20: Reporters notice more worms during media event. Department 'does not rule out' possibility people introduced the worms.

August 21: Department closes three indoor pools after failing to identify worms source.

August 23: All Kowloon Park pools are closed for cleaning and inspection. Children's ppol at Tai Wan Shan, near Hunghom, closes after discovery of several dead worms.

August 24: A Kwun Tong children's pool closes after discover of worms. Inspection fails to find more

August 25: Department calls in police after discovering more worms at Kwun Tong, closes all pools at the complex.