For more than 30 years, pieces of Garfield telephones kept washing ashore on the beaches of northwestern France, and no one quite knew why. Where was the lasagne-loving cartoon cat coming from?

The mystery would puzzle the locals for years. His plastic body parts, first appearing in a crevice of the Brittany coast in the mid-1980s, kept returning no matter how many times beach cleaners recovered them. Sometimes they would find only his lazy bulging eyes, or just his smug face, or his entire fat-cat body, always splayed out in the sand in a very Garfield fashion.

From the stray curly wires and the occasional dial pad, it was clear that the pieces came from the once-popular Garfield telephone, made by Tyco in the early 1980s, several years after Jim Davis first coloured the famously lazy cat into his hit comic strip.

The phone parts were in remarkable condition, considering they had been belched from the ocean, Claire Simonin-Le Meur, president of the environmental group Ar Viltansoù, told The Washington Post. Even Garfield's black stripes were still painted onto his back, where the phone hooked.

She had been searching for the origin of Garfield for years, she said, out of concern for the damage the plastic phones may be doing to the ocean – and this month, after a chance encounter on the beach, she was about to get some answers.

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Ms Simonin-Le Meur said the common belief among locals was that the phones came from a wayward shipping container that must have sunk to the bottom of the ocean, leaving environmentalists to fear Garfield's plastic toxicity would continue to pollute the ocean indefinitely. In 2018 alone, at least 200 pieces of Garfield had been found on beaches in northwestern France, Franceinfo reported.

If they could just salvage the long-lost shipping container, Ms Simonin-Le Meur said, perhaps Garfield would stop coming.

"We were looking for it, but we had no precise idea of where it could be," Ms Simonin-Le Meur said. "We thought it was under the sea. We asked people who were divers to look for it. We get a lot of submarines in the area too – it's a military area. But they said it was not possible the container could be there and nobody saw it."

This year, however, something changed. Ms Simonin-Le Meur got a tip.

It came from a local farmer named René Morvan.

All of Franceinfo's recent publicity of the bizarre phenomenon and its environmental impact had apparently sparked his memory. One day last month, Ms Simonin-Le Meur said she met Mr Morvan on the beach while cleaning up debris – including a Garfield part.

"Are you looking for Garfield?" the man asked.

Ms Simonin-Le Meur said yes, she was – she always was.

"Come with me," the man told her. "I can show you."

Mr Morvan started from the beginning. Back when he was 19 or 20 years old in the mid-1980s, he told her, a storm blew through the area – and before residents knew it, Garfield telephones were scattered all over the beach, just as Ms Simonin-Le Meur had always been told. He and his brother were curious, Mr Morvan said, and they decided to go exploring, touring the rocky coastline until they found what they were seeking.

Wedged inside a cave, tucked into the seaside cliffs, there it was: a metal shipping container – and a cache of Garfield telephones, Mr Morvan claimed he saw.

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The story struck Ms Simonin-Le Meur as too good to be true. The tide was too high to bring her to the cave that day, Mr Morvan realised, and so she would have to wait to find out if he was telling the truth. The shipping container, Mr Morvan told her, was lodged so deep in the cave that it was nearly submerged, making the trip a dangerous expedition.

But finally, last week, it was safe. The tide was low. And Mr Morvan, Ms Simonin-Le Meur said, ultimately was not kidding.

Filming the discovery, a group of journalists and environmentalists, Ms Simonin-Le Meur included, climbed up the rocky shore to the cave's narrow opening, finding snippets of a bright orange phone cord along the way. Garfield was scattered all about, just like on the beach.

But when the group entered the cave, ready for the big reveal, they did not find what they expected. It was clear the plastic cats had been there, Ms Simonin-Le Meur said, but clearer still that most were already gone.

"Our preoccupation was to understand why we had so many Garfields everywhere. We thought it would be helpful to find the container so we can stop it. But that was unfortunately not the case," Ms Simonin-Le Meur said. "What we found was the remainder of the shipping container. And it was empty."

It seemed the group had solved the mystery, she said, but not the problem.

The "Téléphone Garfield," as it is known in an online catalogue for ubiquitous ocean debris, is just one plastic item among countless others that litter the ocean and the shore every year. In the region of northwestern France, the Garfield phone has become like an unwitting Smokey Bear, the mascot for the importance of ocean clean-up and the dangers of microplastics polluting the ocean. Lionel Lucas, who developed the online Ocean Plastic Tracker that catalogues discoveries of Garfield, told Franceinfo the Garfield phone was a "symbol" for the movement.

"It is no longer garbage but evidence," Mr Lucas said.

Ms Simonin-Le Meur said she has tried to use Garfield particularly as a way to interest children in ocean pollution, given its allure compared to pieces of plastic trash. And while the recent purported discovery of Garfield's origins has drawn renewed interest, Ms Simonin-Le Meur said, the discovery did not change much in her eyes.

"We found plastic last Friday and Saturday and Sunday, and we have found a lot of pieces of Garfield," she said. "Things are just exactly the same."