Toxic algae have formed a vast "red tide" off the coast of China, blanketing an area of ocean larger than 1.3 million football fields.
The vast bloom is just the latest manifestation of what the UN has identified as the greatest emerging threat to the health of the seas.
Yesterday, the Chinese government warned people not to eat fish from the area of the bloom in the East China Sea, off the island of Zhoushan Dao, south of Shanghai. Pan Yue, vice-minister at the State Environmental Protection Administration, said: "It might cause damage to people because the red tide contains paralysing toxins."
He added: "The phenomenon, though colourful in appearance, is very dangerous because it can lead to the death of aquatic life and therefore cause damage to the fishing industry."
Red tides - caused by algae feeding on pollution from sewage, fertiliser, car emissions and industrial waste - develop astonishingly fast. Each alga can replicate itself a million times in just two to three weeks until they cover the surface of the sea.
They can suffocate all life, turning parts of the oceans into dead zones.
This spring, a report by the United Nations Environment Programme (UNEP) revealed the number of such zones in the world seas has been doubling every 10 years, as pollution has increased.
Nearly 150 have now been identified - ranging from a third of a square mile to nearly 50,000 square miles. One of the biggest - the size of Scotland - is in the Gulf of Mexico, largely caused by pollution washing down the Mississippi river. Others are in Chesapeake Bay, near Washington, the Black Sea, the Baltic and the northern Adriatic.
UNEP says that the growth of these dead zones is becoming an even greater menace to the life of the sea than the overexploitation which is affecting three-quarters of the world's fisheries.
Dr Klaus Toepfer, UNEP's executive director, says: "Humankind is engaged in a gigantic global experiment as a result of the inefficient and often overuse of fertilisers, the discharge of untreated sewage and the ever-rising emissions from vehicles and factories. "Unless urgent action is taken to tackle the sources of the problem, it is likely to escalate rapidly."Reuse content