The remainder will go to the top performers in four 1,500-metre swimming tests next month.

'Swimmer safety is always our priority concern,' association secretary Ronnie Wong Man-chiu, a winner in the former cross-harbour races that ended in 1978, said. 'If there are any signs or circumstances that may threaten the safety of the swimmers, we will consider postponing the event.'

A key concern is water quality in the harbour, amid reports of a deterioration last year. The route was chosen to avoid pollution and marine traffic, and Wong said careful checks would be made before the race.

He said water quality in the eastern part of the harbour had improved over the past 12 years after the introduction of a deep tunnel sewage collection network and a centralised treatment plant at Stonecutters Island. But some raw sewage from northern Hong Kong Island was still being pumped directly into the harbour.

Wong, who has been in talks with the government for years to plan the event, said the race would be held at high tide when cleaner water from the sea flowed into the harbour from the east, keeping the pollution in central and western waters at bay.

Figures from the Environmental Protection Department show the range of bacteria level, as indicated by the number of E coli units measured at one of the monitoring sites near the race route, ranged between 180 and 4,400 units last year. The bacteria standard for a bathing beach is now set at 610.

The first cross-harbour swim was held in 1906 and the most recent in 1978 when a route between Tsim Sha Tsui pier and Queen's Pier in Central was used. The event was suspended because of pollution and increasing marine traffic.

Wong said he hoped the experience with the revived race would lead to it becoming a full international event.

Ng Yuk-kong, who took part in the most recent cross-harbour race on October 15, 1978, with his friends from a swimming club, said: 'We took it so seriously that we actually hired sampans ... to check the tidal flow and current.'

Ng, 54, recalled that many who wanted to lead the race jumped from the pier into the water and some people were scratched.

He said he would not join this year's race but his 14-year-old son who had entered the Tai Mei Tuk open-water event would enrol. He also said he was not worried about the water quality.

David Chiu Chin-hung, assistant honorary secretary of the association, who took part in the event in the 1960s, said the water at the time was even more worrying than now.

'Rubbish was floating in the sea and the water was not necessarily cleaner than now as everything was also pumped directly into the harbour, too. I believe the water now is much safer,' he said.

The organisers will use about 100 lifeguards to help swimmers in trouble, and there will also be a team of scuba divers to handle emergencies.

Those will fail to reach the finishing point within 95 minutes will be asked to leave the water.

A spokesman for the Marine Department yesterday said there was no need to close the waters to shipping during the race. He said the director of marine would later issue directions for port users on traffic management measures that would ensure the safety of the swimmers.

A spokesman for the Environmental Protection Department said it would closely monitor the water quality before the race.

But a spokesman for the Drainage Services Department said the sewage network did not cover some of the Lei Yue Mun area and some village houses and restaurants might still be using septic tanks to treat waste water. It was not certain if there were any illegal discharges into the sea.