The red tide began off the coast of Zhoushan in East China's Zhejiang Province on May 6, with a detected area of 300 square kilometres, said the local marine environmental monitoring station under the centre Tuesday.

An official with the station, surnamed Tang, noted Tuesday that the red tide is the longest-lasting of the past 10 years and no immediate end was in sight.

A red tide is a dense population of microscopic organisms that breed on the surface of salt water. These organisms, plentiful in number, may suffocate fish by consuming nearly all the oxygen in the water.

Most of the country's red tides occur in April and May and usually last a week or two.

East China Sea areas suffered two large red tides in 2000, measuring around 3,000 and 4,000 square kilometres respectively and lasting a week, said Tang.

The actual coverage of the latest red tide is "surely larger than the measured area," according to Tang.

In recent years, Alexandrium sp. toxic organisms were found in the red tides for the first time, according to Tang. But the latest red tide was caused by the non-toxic organism Prorocentrum dentatum, said Tang.

Tang said the increasing amount of farm pollutants and household waste was a major reason for the frequency of red tides in the East China Sea, in addition to industrial discharges.

He said that no large-scale direct economic losses were being predicted as a result of this month's red tide because it was not near any fish farms. But the damage to the local marine environment will be "enormous," Tang added.

Local media yesterday reported that fish farmers in Zhoushan had taken precautions against the red tide invasion.

Some fish cages have been dropped into deeper water to avoid the red tide, which usually occurs on the surface of the water, said the reports.

To cope with the increasing number of red tides, the State Oceanographic Bureau is preparing to establish 10 red-tide monitoring stations along the coast in Northeast China's Liaoning Province, North China's Hebei Province, East China's Zhejiang and Fujian provinces and South China's Guangdong and Hainan provinces, bureau press officer Wu Jingyou said Tuesday.

The national monitoring network is due to be established by the end of this year. It will provide better forecast services to local fish farmers to prepare for red-tide invasions, according to Wu.

Bureau statistics said the Chinese coast last year suffered 77 severe red tides, covering a total of more than 15,000 square kilometres.

The East China Sea proved to be the most "disastrous" zone, with 27 red tides reported off Zhejiang Province last year.

(China Daily May 29, 2002)