Europe's third sea is dying in humanity's filth

'THE GOLDEN HORN, that deep well surrounded by huge ugly buildings and sooty factories, spewing rust from their chimneys and roofs and walls, staining the water with sulphur-yellow rust, a filthy sewer filled with empty cans and rubbish and horse carcasses, dead dogs and gulls and wild boars and thousands of cats, stinking . . . A viscid, turbid mass, opaque, teeming with maggots . . .'

That is how the Turkish novelist Yashar Kemal describes the most famous creek in the world, that arm of the Bosporus which runs under the walls of Constantinople, or Byzantium, or Istanbul. Nobody knows who first called it the Golden Horn, less still why. It has certainly seen a lot of gold and glory, from the Roman imperial navies to the galley-caiques of the Ottoman sultans. It was closed by a huge iron chain in the reign of Manuel I Comnenus, and the Icelandic sagas tell how the mercenary warrior Harald Sigurdason escaped from the Golden Horn by making his galley leap over the chain.

But it is as filthy as it is glorious. It stinks with good reason. Its banks are lined with boats; ferries arrive and depart; the building boom in Istanbul dumps its debris into it; the sewage of a city of 10 million, increasing at a rate of one person a minute, gushes into it. The Golden Horn has been filthy for more than 2,000 years. But it must now be approaching the stage when - as in the Clyde 100 years ago - the effluent is fierce enough to gnaw through the metal bottoms of ships.

The Bosporus itself, a dark torrent dividing Europe from Asia, is only a few hundred yards across at its narrowest. It has special problems. One is that it gets all the Golden Horn has to bestow. Another is the reckless navigation of the half-trained dipsomaniacs who nowadays seem able to get masters' tickets. Sometimes ships simply drive ashore, a 12,000-ton bulk carrier shouldering unexpectedly on to a cafe terrace. Often they collide. A few weeks back, a Russian ship carrying 20,000 sheep hit a freighter coming down the other way, bang in front of Istanbul, and sank somewhere off the Dolmabahce palace. Some sheep were rescued by lifeboats. Most drowned and rotted.

All this has its results, and they can be measured. Since 1958, the mollusc population in the Bosporus has fallen by more than 82 per cent, Polychaeta worms by 19.4 per cent, sea urchins by nearly 16 per cent. The ecological larder is emptying, in other words, and some fish species are beginning to fall away. And after them come the porpoises and dolphins, which eat the fish.

One of the central figures in Kemal's The Sea-Crossed Fisherman is Fisher Selim, whose mission is to save the dolphins of the Sea of Marmara (into which the Bosporus opens at its western end). These days, people moan about the loss of the dolphins of their youth. So I was all the more amazed when, on a boat trip organised by the Mayor of Greater Istanbul, five or six shiny black fins rolled over in the water beside us. The mayor and his staff were almost as amazed as we were, but pretended not to be. 'But of course,' said the mayor's adviser. 'The results of our new sanitation policies]'

If the boat had run on a few more miles to the east, we would have found ourselves in the Black Sea. This remains one of the strangest waters on earth: Europe's 'Third Sea', after the Mediterranean and North Sea, but far the least known.

Below about 150m-200m, the Black Sea is dead. Nearly 90 per cent of its water mass is 'anoxic' - without oxygen, saturated with hydrogen sulphide gas. It is deep in places, more than 2,200m. But life exists only in this thin top layer. The Black Sea is a gigantic pond: some of the biggest rivers of Eurasia flow into it - Danube, Dnieper, Dniestr, Don - but its only outflow is the thread of the Bosporus.

This deadness is, for once, not the fault of human beings. The Black Sea depths were lifeless when Jason and the Argonauts rowed after the Golden Fleece, when the Vikings from Kiev sailed across to attack Constantinople, when the Light Brigade careered along the Crimean shore. But the catastrophe which is now taking place in the Black Sea, in that precious top layer which once swarmed with life - that is entirely our fault.

Out of 26 species of commercial fish being landed in the 1960s, only six remain in quantities worth netting. The migrating hamsi anchovy, which passes in vast shoals along the north coast of Turkey, provided 320,000 tons of fish in 1984: in 1991 that catch shrivelled to a mere 15,000 tons and there is now a ban on commercial fishing from April to September. Monstrous plankton blooms are appearing in the shallow north-western shelf of the Black Sea (off Ukraine, Moldova and Romania). Light penetration in the increasingly murky waters has fallen from 50-60m to 35 or even 10 near the coasts, killing off creatures which live on the shallow sea floor. Of one main species of sea- weed on the north-western shelf, 95 per cent has been destroyed.

Those are the facts. They mean that, for the first time, man is about to exterminate life in an entire sea. Not all life - sterile algae and jelly-like creatures will occupy the Black Sea. But the living creatures the human race grew up with - those billions of silvery fish migrating round the same track since the last Ice Age, those grinning dolphins whom the Greeks appointed patrons of Trebizond - are about to leave us.

It is detergents, fertilisers, sewage. Above all, it is the Danube. Its phosphate discharge into the sea multiplied by 21 times in 15 years. It carries down every year the incredible quantity of 50,000 tons of oil: enough (as the marine biologist, Laurence Mee, calculates) to pay for an emergency rescue programme for the whole Black Sea. Overfishing does damage; so does the dumping of toxic waste and the damming of rivers. But the Danube accounts for more than half the entire river flow into the Black Sea. It carries the effluent of Germany, Austria, Slovakia, Hungary and Serbia, before coming to Bulgaria and Romania, which have Black Sea coastlines.

At Trebizond (now Trabzon), I walked through the empty fishmarket where stall-holders make do with farmed rainbow trout. I swam in the sea, zigzagging among drifts of foul paper and sewage. I listened to the clamour of boatyards where Turkish fishermen were using government subsidies to build even bigger, more annihilating trawlers. I talked to Professor Celikkale at the Technical University, who said: 'The Black Sea belongs to the world. Even the countries round the sea cannot cope by themselves. This is an international crisis, which needs international money.'

The great rivers are killing the Black Sea. But once they gave it life. Their outrush of water, rich in organic nutrients, bred swarming marine creatures in the warm, shallow dish of the sea's top layer. And in that dish was cooked our own primal soup. The seething fish drew the Greek colonists out of their Aegean villages into a vast outside world of forest, steppe, mountain and ocean. What they took from that world, and what they gave in exchange, combined to found the world we live in now. We can still rescue the Black Sea, and we should.