More than 10,000 people have been mobilized in the Chinese city of Qingdao to clean up green algae which have invaded the Olympic sailing venue.
The algae arrived in late May and now cover 5,000 square miles of sea, the official Xinhua news agency said.
Qingdao's 'green' beachesQingdao's 'green' beaches
BBC video from Qingdao
Algae occupy almost a third of the area that will be used for the sailing competition during the Olympic Games in August. Officials estimate that the clean-up will take two more weeks.
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At a news conference on Sunday, Qingdao Olympic Sailing Committee member Yuan Zhiping said workers were focusing on the competition area.
"We have stressed to all the people devoted to this campaign that the priority should [be] given to the Olympic venue and we expect to eliminate all these sea weeds before 15 July," he said.
Olympic sailors were already training in the area and their preparation was being affected, Xinhua said. More than 1,000 boats were involved in the clean-up operation and 100,000 tonnes of the weeds had already been removed, it added.
Coastal areas and lakes in China see frequent algae blooms, often caused by the discharge of nitrogen-rich chemical pollutants, sewage and fertilizers in the water. But Wang Shulian, of Qingdao's Oceanic and Fishery Department, put the presence of the algae down to the temperature of the water and its salinity.