BEIJING — China has called in thousands of people to clean up an algal bloom at the sailing venue for this summer's Olympic Games, a state news agency said.

The blue-green algae blossomed around June 1 in the waters around Qingdao on the coast of Shandong province, and some 400 boats and 3,000 people have been mobilized to clean it up, the Xinhua News Agency said.

Telephones at the Qingdao Ocean and Fishing Bureau, which is overseeing the cleanup efforts, were not answered Thursday.

Chinese news photos showed the bright-green bloom along the shores of downtown Qingdao. Other images showed workers loading the algae onto boats as windsurfers sailed in the background. The photos also showed people wading in the water and scooping up armfuls of the plant-like organism and putting it into white sacks.

Blue-green algae blooms when nutrients, sometimes caused by excessive pollution, build up in water.

The country's three-decade economic boom has left its waterways and coastlines severely polluted by industrial and farm chemicals and domestic sewage.

About a quarter of the entire population lacks access to safe drinking water and, despite repeated government pledges of a cleanup, the situation is worsening.

Some algae can produce dangerous toxins and if ingested can cause vomiting, respiratory failure and, on rare occasions, death.