The algae that threatened the Olympic Games sailing venue last year has reappeared in the Yellow Sea off the eastern Chinese province of Shandong, local authorities said Monday.

The algae bloom, covering about 42 square kilometers, was drifting north at 9 km per day and was some 120 km from Dagong island of the coastal Qingdao city by Monday, said an official with the North China Sea Branch of the State Oceanic Administration (SOA).

Algae bloom worried officials in the co-host city of the Games last year. At the peak of the outbreak, the algae covered 32 percent of the sailing venue.

More than 1 million tonnes of algae were cleared by 10,000 troops and volunteers, before the sailing events were held smoothly.

An office tackling algae bloom was set up under the SOA. Three ships have been dispatched since this February to research algae, provide data for clean-up and monitor its spread.

(Xinhua News Agency June 16, 2009)