HOFMAN: The city of Qingdao in northern China was just weeks off hosting the sailing regatta for the 2008 Olympics, when its shoreline was engulfed by an outbreak of a thick seaweed known as enteromorpha prolifera.

The outbreak, or "green tide", was the largest ever recorded in the world and covered over 600 square kilometres.

It took 10,000 soldiers from the People's Liberation Army almost two weeks to shift over half-a-million tonnes of the seawood off the beaches.

The country's first ever green tide had been recorded just one year earlier. Since then, there has been one every single year.

Efforts to clean-up the latest, covering 400 square kilometres, are currently underway.

Songdong Shen from the Soochow University in Suzhou has been studying the green tide phenomenon closely, and outlines the factors affecting their frequency:

SHEN: Wind, sunlight, tides, but pollution is the main reason I think. If the pollution continues the outbreak will be more and more serious. the ecological element of the sea area would be ruined seriously because the biomass of enteromorpha prolifera is huge and a lot of oxygen are consumed by them.

HOFMAN: And when enteromorpha prolifera uses up the oxygen, it leaves little for the other marine species in the area.
That's a serious concern, and one that has prompted scientists across the country and abroad to look at the issue more closely.

Among them is Dr John Keesing from Australia's Commonwealth Scientific and Industrial Research Organisation, the C-S-I-R-O.

The seaweed needs warm, calm weather conditions and nutrients to multiply, but Dr Keesing says there's another increasingly present factor contributing.

KEESING: What you've had happen fairly recently in China is an extensive expansion of coastal aquaculture and in particular, the aquaculture of porphyra or nori. It's what's commonly used to wrap around your sushi and what we've found is that you get very high accumulation of this pest algae, this ulva or enteromorpha which causes the green tides growing on the rafts. So, it's not the actual nori that's causing the green tide but the enteromorpha grows on the bamboo and poles that are used to construct the raft.

HOFMAN: Greenpeace China says it believes the problem will get worse unless the government considers taking serious action.

Campaigner Pan Wenjing says the government is deliberately ignoring the issue.

WENJING: Shandong province is a very large and important agricultural region in China but the agriculture approach is actually the very polluted, intensive, chemical agriculture which heavily relies on the input of chemical fertiliser. The overuse results in lots of nitrogen flow into the river and this becomes the nutrition for the algae. The government knows the pollution is there but China is really heavily reliant on the fertiliser to ensure the food yield but actually if there is no immediate change on the agriculture approach the pollution will be very, very difficult to deal with.