A third of the 50 sq km sailing course is now covered by a bright green layer of algae, giving an embarrassing twist to the government's promise to host an environment-friendly 'Green Olympics'.

The official Xinhua news agency said more than 10,000 people and thousands of vessels had been mobilised 'nationwide' for a massive cleaning operation.

Nine provinces and municipalities have also sent 18,000m of oil buffers to Qingdao so that it can build a 32,000m marine fence around the sailing course and prevent more algae from flowing in.

Qingdao aims to nick the problem by July 15. But with sailors from at least 30 countries already in town for training before official competition begins, the public relations damage is all but done.

Media reports said one team's sailboat got stuck so badly that it had to be hauled out by a local fishing boat. The Associated Press quoted a Greek sailing team member calling the sludge 'a green nightmare'.

Officials however said the stadiums and competition venues in Beijing, located about 550km away from Qingdao, would not be hit by such algae blooms, which are sometimes caused by excessive pollution.

'The water bodies associated with the stadiums will not experience algae blooms during or after the Olympics,' Mr Bi Xiaogang, deputy director of the Beijing Water Authority, told reporters at a press conference yesterday.

The only major outdoor water-based competition venue in Beijing is the Shunyi Olympic Rowing-Canoeing Park. But some venues, such as the iconic Bird's Nest stadium, are ringed by man-made lakes for aesthetic reasons.

chinhon@sph.com.sg