When 28,800 bath toys fell off a cargo ship in the Pacific 20 years ago, they began an incredible journey. While some washed up in British Columbia and Hawaii, countless others circumnavigated the globe. Here, in an excerpt from his new book, Donovan Hohn follows the fantastic voyage

At the outset I felt no need to acquaint myself with the six degrees of freedom. I'd never heard of the Great North Pacific Garbage Patch. I liked my job and loved my wife and was inclined to agree with Emerson that travel is a fool's paradise. I just wanted to learn what had really happened, where the toys had drifted and why. I loved the part about containers falling off a ship, the part about the oceanographers tracking the castaways with the help of far-flung beachcombers. I especially loved the part about the rubber duckies crossing the Arctic, going cheerfully where explorers had gone boldly and disastrously before.

At the outset I had no intention of doing what I eventually did: quit my job, kiss my wife farewell, and ramble about the northern hemisphere aboard all manner of watercraft. I certainly never expected to join the crew of a 51ft catamaran captained by a charismatic environmentalist, the Ahab of plastic hunters, who had the charming habit of exterminating the fruit flies clouding around his stash of organic fruit by hoovering them out of the air with a vacuum cleaner.

We know where the spill occurred: 44.7°N, 178.1°E, south of the Aleutians, near the International Date Line, in the stormy latitudes renowned in the age of sail as the Graveyard of the Pacific, just north of what oceanographers call the subarctic front. We know the date – 10 January 1992 – but not the hour.

For years the identity of the ship was a well-kept secret, but by consulting old shipping schedules published in the Journal of Commerce and preserved on scratched spools of microfiche in a library basement, I, by process of elimination, solved this riddle: the ship was the Evergreen Ever Laurel, owned by a Greek company called Technomar Shipping and operated by the Taiwanese Evergreen Marine Corp.

We know that the ship departed Hong Kong on 6 January, that it arrived in the Port of Tacoma on 16 January, a day behind schedule, and that the likely cause for this delay was rough weather. How rough exactly remains unclear. Although it did so on other days, on 10 January the Ever Laurel did not fax a weather report to the National Weather Service in Washington DC, but the following morning a ship in its vicinity did, describing hurricane-force winds and waves 36ft high.

If the Ever Laurel had encountered similarly tempestuous conditions, we can imagine, if only vaguely, what might have transpired: despite its grandeur, rocked by waves as tall as houses, the colossal vessel – a floating warehouse weighing 28,904 deadweight tons and powered by a diesel engine the size of a barn – would have rolled and pitched and yawed about like a toy in a Jacuzzi.

At some point, on a steep roll, two columns of containers stacked six high above deck snapped loose from their steel lashings and tumbled overboard. We can safely assume that the subsequent splash was terrific, like the splash a train would make were you to drive it off a seaside cliff.

We know that each of the 12 containers measured 8ft wide and either 20ft or 40ft long, and that at least one of them – perhaps when it careened into another container, perhaps when it struck the ship's rails – burst or buckled open as it fell.

We know that as the water gushed in and the container sank, dozens of cardboard boxes would have come bobbing to the surface; that one by one, they too would have come apart, discharging thousands of little packages on to the sea; that every package comprised a plastic shell and a cardboard back; that every shell housed four hollow plastic animals – a red beaver, a blue turtle, a green frog and a yellow duck – each about 3in long; and that printed on the cardboard in colourful letters in a bubbly, childlike font were the following words: THE FIRST YEARS. FLOATEES. THEY FLOAT IN TUB OR POOL. PLAY & DISCOVER. MADE IN CHINA. DISHWASHER SAFE.

From a low-flying plane on a clear day, the packages would have looked like confetti, a great drift of colourful squares, exploding in slow motion across the waves. Within 24 hours the water would have dissolved the glue.

The action of the waves would have separated the plastic shell from the cardboard back. There, in seas almost four miles deep, more than 500 miles south of Attu Island at the western tip of the Aleutian tail, more than 1,000 miles east of Hokkaido, the northern extreme of Japan, and more than 2,000 miles west of the insular Alaskan city of Sitka, 28,800 plastic animals produced in Chinese factories for the bathtubs of America – 7,200 red beavers, 7,200 green frogs, 7,200 blue turtles and 7,200 yellow ducks – hatched from their plastic shells and drifted free.

Curtis Ebbesmeyer has reconstructed the drift routes of the toys, using an ocean surface current simulator. Photograph: Dave Ingraham

On Thanksgiving Day 1992 a party of beachcombers strolling along Chichagof Island, off the coast of Alaska, discovered several dozen hollow plastic animals amid the usual wrack of bottle caps, fishing tackle and driftwood deposited at the tide line by a recent storm. After 10 months at sea, the ducks had whitened and the beavers had yellowed, but the frogs were still green as ever, and the turtles still blue.

On the windward side of Chichagof, as on other islands near Sitka, the beachcombers found toys, hundreds of them – frogs half-buried under pebbles, beavers poised atop driftwood, turtles tangled in derelict fishing nets, ducks blown past the tide line into the purple fireweed. Beachcombing in the Alaskan wilderness had suddenly come to resemble an Easter egg hunt.

Laurie Lee of South Baranof Island filled a skiff with the hoard of toys she scavenged. Signe Wilson filled a hot tub. Betsy Knudson had so many to spare she started giving them to her dog. It appeared that even the wild animals of Sitka Sound were collecting them: one toy had been plucked from a river otter's nest. On a single beachcombing excursion with friends, Mary Stensvold, a botanist, gathered 40. Word of the invasion spread.

Toys had been found as far north as Kayak Island, as far south as Coronation Island, a range extending hundreds of miles. Where had they come from? Eben Punderson, a high-school English teacher who moonlighted as a journalist on the Daily Sitka Sentinel, was pretty sure he knew. Three years earlier, in May 1990, an eastbound freighter, the Hansa Carrier, had collided with a storm 500 miles south of the Alaskan Peninsula. Several containers had gone overboard, including a shipment of 80,000 Nikes. Five months later, trainers began washing up along Vancouver Island.

The story received national attention after two oceanographers in Seattle – James Ingraham of the National Oceanographic and Atmospheric Administration (NOAA) and Curtis Ebbesmeyer, a scientist with a consulting firm that assessed the environmental risks and impacts of engineering projects (sewage outflows, oil rigs) – turned the trainer spill into an accidental oceanographic experiment. By feeding coordinates collected from beachcombers into NOAA's Ocean Surface Current Simulator, or Oscurs, a computer modelling system built from a century's worth of US Navy weather data, Ebbesmeyer and Ingraham had reconstructed the drift routes of some 200 shoes.

The basement of Ebbesmeyer's bungalow had become the central intelligence agency of what would eventually grow into a global network of coastal informants. If anyone knew anything about the plague of plastic animals it would be Ebbesmeyer – but when the Sentinel's moonlighting reporter contacted him in the summer of 1993, it was the first the oceanographer had heard of the toys.

Punderson still had another lead. The ducks – and for some reason only the ducks – had been embossed with the logo of their manufacturer, The First Years. A local toy shop was unable to find the logo in its merchandise catalogues, but the director of the Sheldon Jackson College library traced the brand back to its parent company, Kiddie Products, based in Avon, Massachusetts. Punderson spoke to the company's marketing manager, who somewhat reluctantly confirmed the reporter's speculations. Yes, indeed, a shipment of Floatees had been lost at sea.

"Solved: Mystery of the Wandering Bathtub Toys" ran the lead headline in the Sentinel's Weekend section. And that is where the story should have ended – as an entertaining anecdote in the back pages of a provincial newspaper. But then something else unexpected happened. The story kept going.

Oscurs could now reconstruct, or "hindcast", the routes the toys had travelled, producing a map of erratic trajectories. Beginning at the scattered coordinates where beachcombers had reported finding toys, the lines wiggled west, converging at the point of origin: 44.7°N, 178.1°E, south of the Aleutians, near the International Date Line, where farthest west and farthest east meet. The data that Ebbesmeyer's beachcombers had gathered also allowed NOAA's James Ingraham to fine-tune the computer model, adjusting for such coefficients as "windage" (an object with a tall profile will sail before the wind as well as drift on a current).

Before they'd sprung leaks and taken on water, the toys rode high, skating across the Gulf of Alaska at an average rate of seven miles per day, almost twice as fast as the currents they were travelling. In 1992 those currents had shifted to the north as a consequence of El Niño. If the toys had fallen overboard at the same spot just two years earlier, they would have taken a southerly route instead of a northerly one, ending up in the vicinity of Hawaii. In 1961 they would have drifted along the California coast. As Oscurs could forecast as well as hindcast, Ebbesmeyer and Ingraham were like meteorologists of the waves. Because the weather of the ocean usually changes more slowly than the weather of the skies, they were also like clairvoyants. Oscurs was their crystal ball.

By simulating long-term mean surface geostrophic currents (those surface currents that flow steadily and enduringly, though not immutably, like rivers in the sea) as well as surface-mixed-layer currents that are functions of wind speed and direction (those currents that change almost as quickly as the skies), Oscurs could project the trajectories of the toys well into the future.

According to the simulator's predictions, some of the animals that remained afloat would drift south, where they would collide with the coast of Hawaii in March 1997, or get sucked into the North Pacific Subtropical Gyre. "Gyre is a fancy word for a current in a bowl of soup," Ebbesmeyer likes to say. "You stir your soup, it goes around a few seconds." The thermodynamic circulation of air, which we experience as wind, is like a giant spoon that never stops stirring.

To make Ebbesmeyer's analogy more accurate, you'd have to set that bowl of soup aspin on a lazy Susan, since the earth's rotation exerts a subtle yet profound influence on the movements of water and air. The North Pacific Subtropical Gyre revolves between the coasts of North America and Asia, from Washington State to Mexico to Japan and back.

Some of the toys, Oscurs predicted, would escape the gyre's orbit, spin off toward the Indian Ocean, and circumnavigate the globe. Others would drift into the gyre's becalmed heart where the prevailing atmospheric high has created what Ebbesmeyer christened "the Garbage Patch" – a purgatorial eddy in the waste stream that covers, he told me, as much of the earth's surface as Texas. He pointed out that there are in fact many garbage patches in the world, the one in the North Pacific being simply the largest. He referred to it as the Great North Pacific Garbage Patch. "It's like Jupiter's red spot," he said. "It's one of the great features of the planet Earth, but you can't see it."

Down at South Point, Hawaii, after dropping off my suitcase at the Shirakawa Motel and driving south in my rental car, after reaching the end of the road and continuing on foot, I begin to see what I've come looking for – the colourful confetti of plastic debris. In almost every cove formed by black lava rock there are drifts of it, piled up in crescents many feet deep.

There's fishing gear, shattered fishing floats, tangles of nets, but if you stop and stoop down and look closely you can pick out more commonplace objects – detergent bottles, Nestlé lids, golf balls. The coves sort the plastic. In one there's an abundance of jar lids. In the next an abundance of nets. In another dozens of plastic ice lolly sticks. Do fishermen like lollies? Or did these belong to children on a seaside holiday? I don't find any Floatees.

The next morning I station myself in the motel courtyard. A silver pickup truck arrives. At the wheel is Bill Gilmartin, a retired, ponytailed biologist formerly employed by the National Marine Fisheries Service. On the door of his truck is a sign that reads HAWAII WILDLIFE FUND. Gilmartin paid mechanics to turn his pickup truck into a dump truck. The bed, hoisted by some sort of hydraulic mechanism, can tip. I climb into the passenger seat and we zoom south, bound for Kamilo Beach.

"I started out in debris collection on the Northwestern Hawaiian Islands in 1982," Gilmartin says. "You get into this business in your gut and your heart and it's hard to back out."

Here are windmills and a cracked road leading to the end of the world, or at least to the edge of the United States. Tarmac gives way to dirt. We ramble along the red dirt road, and soon enough we've travelled farther than I made it the day before on foot. "This coast is so bad," Gilmartin says, "debris comes up faster than you can keep it clean. It gets continuous onshore winds and it's in the way of the easterly currents." By his calculations, 20 tons of trash wash up along the eastern coast of South Point every year. "Even if everything stopped today, it would keep washing in." Gilmartin can't think of a better way to spend the weekends of his retirement than this – hauling debris in his truck.

We come to a pile of blue bags. Gilmartin and I hurl these into his truck. Then a big mess of derelict net, which he hooks to his winch. At last the tyres of Gilmartin's truck crackle up to the edge of Kamilo Beach – a beach of plastic, finely ground. There are twigs of driftwood, and igneous pebbles, and a few coconuts, but they're far outnumbered by the shrapnel of debris. This is where the flotsam I saw yesterday ends up. The surf and sun grind it down and the currents deposit it here, and here, until a flood tide or a storm surge sweeps it out to sea, it remains; Gilmartin can't bother with the plastic sand. There's simply too much of it.

It's almost beautiful, all those unnatural colours and shapes in such a natural landscape, beautiful because incongruous. This is what I have been pursuing these past months; this is what I found so spellbindingly enigmatic about the image of those plastic ducks at sea – incongruity. We have built for ourselves out of this New World a giant diorama, a synthetic habitat, but travel beyond the edges or look with the eyes of a serious beachcomber and the illusion begins to crumble like flotsam into sand. Incongruities emerge, and not just visual ones.

For instance: in 1878, nine years after its invention, a sales brochure promoted celluloid as salvation. "As petroleum came to the relief of the whale," the copy ran, so "has celluloid given the elephant, the tortoise, and the coral insect a respite in their native haunts; and it will no longer be necessary to ransack the earth in pursuit of substances which are constantly growing scarcer."

Ninety years later, in the public mind, plastic had gone from miracle substance to toxic blight. In 1968, at the dawn of the modern environmental movement, the editor of Modern Plastics argued that his industry had been unfairly vilified. Plastic was not the primary cause of environmental destruction, he wrote, only its most visible symptom. The real problem was "our civilisation, our exploding population, our lifestyle, our technology".

That 1878 sales brochure and that 1968 editorial were both partly, paradoxically right. Petroleum did save some whales; plastics did save the elephant, not to mention the forest. Modern medicine, personal computing and safe, fuel-efficient cars would not exist without them. They consume fewer resources to manufacture and transport than most alternative materials do. Even environmentalists have more important things to worry about now. In the information age, plastics have won. We have banished all thoughts of drift nets and six-pack rings, and what lingering anxieties remain we leave at the curbside with the recycling.

Never mind that only 5% of plastics actually ends up getting recycled. Never mind that the plastics industry stamps those little triangles of chasing arrows into plastics for which no viable recycling method exists. Never mind that plastics consume 400m tons of oil and gas every year and that oil and gas will in the not-too-distant future run out. Never mind that so-called green plastics made of biochemicals release greenhouse gases when they break down.

What's most nefarious about plastic is the way it pretends to deny the laws of matter, as if something could be made from nothing; the way it is intended to be thrown away but chemically engineered to last. By offering the false promise of disposability, of consumption without cost, it has helped create a culture of wasteful make-believe, an economy of forgetting.

At Plastic Beach I scoop up a handful of multicoloured sand and sift it through my fingers. This then is the destiny of those toy animals that beachcombers fail to recover: baked brittle by the sun, they will eventually disintegrate into shards. Those shards will disintegrate into splinters, the splinters into particles, the particles into dust, the dust into molecules, which will circulate through the environment for centuries.

The very features that make plastic a perfect material for bathtub toys also make it a superlative pollutant of the seas. No one knows exactly how long a synthetic polymer will persist at sea. Five hundred years is a reasonable guess. Globally we are producing 300m tons of plastic a year, and no known organism can digest a single molecule of the stuff, though plenty of organisms try.

This is an edited extract from Moby-Duck: The True Story of 28,800 Bath Toys Lost at Sea by Donovan Hohn (Union Books, £20). To order a copy for £16 with free UK p&p click on the link or call 0330 333 6846