ODESSA, Ukraine -- Flooded with pollutants from land, sea and air; wracked by civil war on one coast, packed with tourists on others; trapped in the middle of one of the world's great political and economic transformations -- the Black Sea, the dirtiest in the world, is dying an agonizing death.


In merely 30 years, the sea, famed since the times of Ovid and Herodotus for its rough storms and rougher inhabitants, has degenerated from one of the world's most productive bodies of water to a toilet bowl for half of Europe -- a dumping ground for vast quantities of phosphorus, inorganic nitrogen, oil, mercury and DDT generated by the 160 million people living in the Black Sea basin.


In a region struggling to come to terms with an environmental crisis following decades of rule by centrally planned economies notorious for their disregard for nature, the death of the Black Sea would be a major defeat in efforts to clean up the mess left by communism. For the world as a whole, the demise of the Black Sea -- bigger than any body of water to die so far -- would stand as a chilling prophecy for other seas.


Of the 26 species of fish caught in the Black Sea by fishermen in the 1960s, only five remain. Mackerel, once the mainstay of the fishing industry, were last fished commercially in 1965. In less than 10 years, the total catch has plummeted from nearly 700,000 tons a year to 100,000 tons.


More than 1 million dolphins frolicked in the Black Sea 30 years ago; now the population has dropped to about 200,000. Many of them are infected with swine fever -- probably passed on by waste from pig farms up the Danube River delta. Monk seals have disappeared. Oysters and blue mussels, known as the kidneys of the sea because they filter its water, also are vanishing. The sea's lungs -- rich meadows of beneficial forms of bottom-growing algae and sea grass that occupied 10,920 square kilometers along the sea's once fecund northwest shelf -- have shrunk to one-tenth their previous size.


Since the 1970s, cholera outbreaks have become routine, because sewage treatment plants are almost non-existent. Beaches throughout the region, the only warm-water vacation area in the former Soviet Union, are regularly shut by foul-smelling pollution and suffocating blooms of harmful surface algae and other phytoplankton. One such bloom killed an estimated 50 percent of bottom-feeding fish along Romania's coast in 1991, turning beaches around Constantsa into a "long line of death, an apocalypse," according to Radu Mihnea, a biologist at the Romanian Marine Research Institute there.


Against heavy odds, a plan backed by the United Nations and the World Bank began late last year to tie together various projects aimed at saving the Black Sea. Based in Istanbul and led by a British marine biologist, Laurence Mee, the Environmental Management and Protection Program of the Black Sea has a three-year budget of just $25 million to coordinate research and identify urgent cleanup efforts.


This year, Ukraine became the last of the six countries bordering the sea to approve the Black Sea convention that establishes legal tools to control maritime pollution. The six -- Georgia, Russia, Ukraine, Romania, Bulgaria and Turkey -- recently have begun negotiating a second convention that would place quotas on fishing catches. The challenges are huge. Economic disaster and political chaos in the former Soviet republics of Russia, war-ravaged Georgia and tottering Ukraine, and in Bulgaria and Romania, do not bode well for a cleanup that will cost billions.


In June, a meeting was to have taken place among representatives of the six: Only Bulgaria, Turkey and Romania showed up. Russia said its invitation arrived too late; Ukraine begged a lack of funds; Georgia's excuse was civil war.


Formed about 8,000 years ago by shifting tectonic plates, the huge lake of 416,000 square kilometers was suddenly connected to the world's oceans by the Bosporus -- a narrow, 30-kilometer waterway that leads into the Mediterranean. This peculiarity -- similar to an Olympic-sized pool being drained through a keyhole -- has created enormous problems for the Black Sea.


The lack of a good drainage mechanism effectively created two seas -- one of the world's most fertile bodies of water lying atop a huge dead puddle. Below 135 meters, the Black Sea contains no oxygen and supports no life. It is only above that depth that fish and other marine life survive.


The two layers are prevented from blending for much the same reason that oil and water do not mix: the lower half is saltier and denser than the upper, so much so that scientists estimate it would take a molecule on the bottom 100 years to travel to the surface.


Above 135 meters, and especially along its northwest coast, the Black Sea once swarmed with life. Its northern arm, the Sea of Azov, was the second most productive source of fish in the world per acre, after Chesapeake Bay. The whole Black Sea was five times more productive per acre than its larger neighbor, the Mediterranean.


Immense meadows of red algae on the shelf's bottom served up huge doses of agar, which is used as a base for bacterial cultures, as well as natural dyes and raw materials for pharmaceuticals. Bays and inlets boasted large catches of blue mussels and oysters. They also swarmed with shrimp, crab, sturgeon, stingrays, gobies, shad, bonito, mackerel and mullet. In all, more than 2 million people lived off Black Sea fishing.


"We were crazy with fish," recalled Nikolai Prodaivoda, 51, a fisherman at the Black Sea collective fish farm in Vapnjarka, a village 20 miles north of Odessa where the motto "Our Goal Is Communism" still adorns the wall of a dilapidated boathouse.


Prodaivoda's work brigade used to haul in 20 tons a day. Now it is lucky to get 700 pounds. Fishermen have taken to metalworking and construction. When Prodaivoda pulls up the nets, oil often covers the top. The bottom reeks of rotten eggs, from hydrogen sulphide, another product of the dying sea. Sometimes there is so much acid in the water his hands blister and peel.


"My son wants to be a fisherman," Prodaivoda said, tousling the blond hair of Viktor, 9. "I don't think there's a future."