BEIJING Chinese authorities have dispatched a flotilla of more than 60 ships to head off a massive tide of algae that is approaching the coast of Qingdao, north east China.

The outbreak is thought to be caused by high ocean temperatures and excess nitrogen runoff from agriculture and fish farms.

Scientists involved in the operation say the seaweed, known as enteromorpha, needs to be cleaned up before it decomposes on beaches and releases noxious gases.

According to the domestic media, the green tide covers an area of 400 sq km. Newspapers ran pictures of coastguard officials raking up the weed as soon as it reached the shore.

As well as the 66 vessels sent to intercept the approaching algae, a net has been stretched offshore as an extra defence. Ten forklift trucks, seven lorries and 168 people were clearing up the many tonnes of seaweed that still got through.

Li Delin, the engineer in charge of the beach clearance, estimated that his team had collected about 3,900 tonnes as of Wednesday. The seaweed has been taken away to be processed, possibly for use as natural fertiliser or animal feed. And more is on the way. Northern China has been experiencing the hottest week of the year - in some areas, such as Beijing, temperatures have reached highs not seen in decades - which was accelerating the growth of the algae.

Green and red tides have become increasingly common across the world since the 1970s. Usually they occur in coastal water near densely populated areas or where there is large-scale runoff of agricultural chemicals from farmland.

China has been particularly affected in recent years. An even bigger outbreak off Qingdao, estimated at 170,000 tonnes, in 2008 threatened to ruin the sailing events for the Olympics, prompting the authorities to call on hundreds of local fishermen to help them in the cleanup operation.

The green tide is a sign of eutrophication, a build-up of algae caused by excess levels of nitrogen in the water. At low levels this simply means a green slime on the water's surface, such as that often seen on polluted lakes.

In its worst form, the algae can be toxic or so dense that it chokes the life below it, creating underwater “dead zones”.

The green tide approaching Qingdao is harmless in its current form and, if quickly dealt with, could even help to clean up the coastal waters.

Li said that given the size of the algae plume, it would be unwise to let it decompose naturally. “If the enteromorpha on the beach can't be cleared on time, it will rot and affect the ecosystem in the bay area. Also the smell will be really bad,” he said.

Preventing future algae outbreaks is a challenge. Scientists have advised the government to discourage overuse of fertiliser and to build more water treatment plants. But many experts believe the cause is deeper.

“At a fundamental level, the way to deal with this should be to combat climate change and control pollution,” said Mao Yunxiang, a professor at the College of Marine Life, Ocean University of China, who is a consultant on the operation.

“We should also consider the possibility that the green tide are inevitable so we should make use of them. The algae can clean water, and be harvested for animal feed and bio-fertiliser.”—Dawn/The Guardian News Service