Workers are racing to remove the algae from Qingdao's coast
More than 10,000 people have been mobilised in the Chinese city of Qingdao to clean up green algae, which have invaded the Olympic sailing venue.
The algae had arrived in late May and now covered 13,000 sq km (5,000 sq miles) of sea, Xinhua news agency said.
They occupy almost a third of the area that will be used for the sailing competition during the 9-21 August Olympic Games.
Officials estimate that the clean-up will take two more weeks.
Richard Zheng from Qingdao told the BBC News website that a number of his fellow students had been involved in the clean-up effort.
"There is really too much algae. When I go to the beach, I can smell it and it is really quite smelly - a bit like a soup we drink in restaurants," he said.
"Some people are getting quite worried in case this will have an impact on the Olympic Games. But there are many fishing ships out collecting the algae as well as students. We believe the algae will disappear when the weather changes.
"This has happened before in Qingdao but not so frequently in the last few years," Mr Zheng added.
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.
Beaches around the city have been smothered by the algae
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 fertilisers 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.