LONDON: Last summer every water creature across a vast area of sea was asphyxiated by severely depleted oxygen levels in the Gulf of Mexico. The same phenomenon, the marine equivalent of the ozone hole , happened off South America, China, Japan, south east Australia, New Zealand, and up to 150 other places.

A United Nations agency warned on Monday that the number of these "dead zones", caused mainly by the run-off of nitrogen fertilizers from intensive farming and sewerage from large cities, had doubled in the past 15 years and was increasing all over the world.

In a new report, the UN environment programme said that 150 sea areas were now regularly starved of oxygen and were becoming major threats to already declining fish stocks, including those in Europe, where areas of the Baltic sea were lifeless for several months, as were parts of the Irish sea and the Adriatic.

The Black Sea - the largest and oldest "dead zone" in the world - supported only a few bacteria to a depth of 150 metres. "Humankind is engaged in a gigantic, global, experiment as a result of the inefficient and often over-use of fertilizers, the discharge of untreated sewage and the ever rising emissions from vehicles and factories," said Klaus Toepfer, the UN environment programme (UNEP) director.

"The nitrogen and phosphorous from these sources are being discharged into rivers and the coastal environment or being deposited from the atmosphere, triggering these alarming and sometimes irreversible effects," he said.

Some of the dead zones are less than one square kilometre, whereas others are up to 70,000 sq km. Many have been found near the outlets of big rivers such as the Mississippi and the Yangtse, which drain huge industrial areas. Most lie off countries which heavily subsidise their agriculture.

"What is clear is that unless urgent action is taken to tackle the sources of the problem, it is likely to escalate rapidly," he said. -Dawn/The Guardian News Service.