To host the Olympic sailing events, the graceful eastern China port city of Qingdao moved a massive boat yard, relocated industries and spent about $850 million on transport links, parks, pollution controls and coastal green belts.

But with a little more than a month to go until the games, a whole different kind of challenge is cropping up: A forest of blue-green algae is choking the coastal waters, suffocating beaches and lying in thick layers along sailing routes.

Authorities have ordered an all-out drive to catch it, clear it, and block any more drifting into the area.

"We have stressed ... that the priority should be given to the Olympic venue," the official Xinhua News Agency quoted Yuan Zhiping, an official with the Qingdao Olympic Sailing Committee, as saying.

City officials say they'll need at least two weeks to clear coastal waters, mobilizing 10,000 workers aboard 1,000 boats. It wasn't clear how they planned to block other algae from drifting in.

Environmental problems have posed some of the biggest last-minute concerns for organizers of the Olympics, particularly the dust and filthy air in the Chinese capital, compounded by expected torrid heat and humidity.

It isn't clear whether Qingdao's Olympic planners ever prepared for algae-related problems during the games. Calls to the city's Ocean and Fishing Bureau, charged with handling the problem, rang unanswered on Monday.

Blue-green algae "blooms" when nutrients, sometimes caused by excessive pollution, build up in water. Such rapid growth can take over entire lakes and choke coastlines.

China has had a number of similar outbreaks in recent years, mostly on inland lakes, largely as a result of severe pollution from industrial sources, farm chemicals and domestic sewage.

Wang Shulian, vice director of the Ocean and Fishing Bureau, told reporters Sunday the Qingdao outbreak had no "substantial link" to environmental conditions or water quality.

"The algae is of various sorts, which will prosper under satisfying temperature and salinity of sea water," Wang was quoted as saying.

The algae is blooming over an area of 5,000 square miles, Xinhua said — including 32 percent of the coastal sea area set aside for the Aug. 9-21 events, with a closing ceremony on Aug. 23.

Officials say the Qingdao blossom poses no health threat. However, some algae can produce dangerous toxins and if ingested can cause vomiting, respiratory failure and, on rare occasions, death.

The cleanup is expected to be completed by July 15, Xinhua reported.