BEIJING - With fewer than six weeks before it plays host to the Olympic sailing regatta, the city of Qingdao has mobilized thousands of people and an armada of small boats to clean up an algal bloom that's choking the coastline and threatening to impede the Olympic competition.

Local officials have launched an intense effort to clean up the algae by mid-month. Media reports estimate as many as 20,000 people have either volunteered or been ordered to participate in the operation, while 1,000 boats are scooping algae out of the Yellow Sea. The country's official news agency, Xinhua, reported that algae covers a third of the coastal waters designated for the Olympic competition.

Water quality has been a concern for the Olympic sailing events, given that many coastal Chinese cities dump untreated sewage into the sea. At the same time, rivers and tributaries emptying into coastal waters are often contaminated with high levels of nitrates from agricultural and industrial runoff. These nitrates contribute to the red tides of algae that often bloom along sections of China's coastline.

But officials in Qingdao said pollution and poor water quality did not have a "substantial link" to the current outbreak, according to Xinhua. Instead, scientists blamed the bloom on increased rainfall and warmer waters in the Yellow Sea. Algae blooms now affect more than 5,000 square miles of sea water, according to Xinhua.

Fencing it in

Yuan Zhiping, an official with the Qingdao Olympics Sailing Committee, told reporters Sunday that the government would attempt to block algae from floating into the Olympic sailing area by installing a 30-mile-long fenced perimeter in the sea.

"I believe we will make sure the Olympics sailing area is clean by July 15 through our efforts," Yuan said, according to the Shandong News Web site.

Photographs in the Chinese media showed rickety wooden boats overflowing with green mounds of algae collected from the sea. One photo showed a young boy crouched on a beach beside piles of the leafy glop as a dump truck carried off a large load of algae. State media reported that 100,000 tons of algae had been taken out of the water. Much of it was being transported to farms as feed for pigs and other animals, according to news reports.

Residents of Qingdao have been anticipating the city's Olympic moment for several years. One local newspaper reported that 11,000 college students had volunteered for cleanup duty over the weekend. Several companies had organized teams of employees to help.

Can't sail through it

The massive outbreak comes as some sailing teams are in Qingdao preparing for the Olympics. Photographs in the Australian press showed an Australian team seemingly stuck in a carpet of algae during a training run. A British windsurfer, Bryony Shaw, who has been training in Qingdao, told the English media that the algae would pose significant problems to the competition if it is not cleaned up.

"There's no way you can sail through it," Shaw said. "If it's still here in August, it could be a real problem."

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