For more than 30 years bright orange "Garfield" phones have been washing up on the French coast to the bemusement of local beach cleaners, who have finally cracked the mystery behind them. Locals had long suspected a lost shipping container was to blame for the novelty landline phones, modelled on the prickly feline cartoon character, that have plagued the northern Finistere beaches for decades.

"Our association has existed for 18 years and in that time we have found pieces of Garfield telephones almost each time we clean," said Claire Simonin, the head of local beach cleaning group Ar Viltansou in Brittany.

But it wasn't until a local resident revealed that he had discovered the container after a storm in the 1980s that they were finally able to locate it -- wedged in a partially submerged cave only accessible at low tide.

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"He told us where it was... it was very, very dangerous," Simonin told AFP after an expedition to track it down.

Spare parts of plastic 'Garfield' phones are displayed on the beach, March 28, 2019 in Plouarzel, western France, after being collected from a sea cave by environmental activists. Getty

"We found this incredible fissure that is 100 feet deep and at the very bottom, there were the remains of a container."

"Under the boulders in front of the entrance, we found 23 complete handsets with electronics and wires. They were everywhere," she added.

But the mystery, first reported by the France Info public broadcaster, is not fully solved.

"We have no idea what happened at the time: we do not know where it came from, what boat," said Fabien Boileau, director of the Iroise Marine Nature Park in Finistere. "And we don't know if several containers fell into the water, or only one."

The dry-witted Garfield, first dreamed up by illustrator Jim Davis in the late 1970s, has since spawned a television show, a film series starring Bill Murray as the voice of the titular cat, and a merchandising empire worth hundreds of millions of dollars annually.

Spare parts of plastic 'Garfield' phones are displayed on the beach on March 28, 2019 in Plouarzel, western France, after being collected from a sea cave by environmental activists. Getty

The discoveries in France highlight the problem of plastic pollution, which has become the subject of a major global environmental campaign in recent years. The world currently produces more than 300 million tons of plastics annually, and there are at least five trillion plastic pieces floating in our oceans, scientists have estimated. Some forecasts predict that there will be more plastic in the seas than fish by 2050.

Even animals living in the deepest ocean trenches have been found with fragments in their gut, according to new research published in February showing how the scourge reached into the bowels of the planet.

Container ships arriving from Asia and elsewhere travel past the northwestern coast of France as they head to the major European ports including Calais, Antwerp or Rotterdam.

In March, the ship "Grande America" sank 300 kilometers west of the town of La Rochelle, spilling 2,000 cars and 365 shipping containers into the ocean, 45 of which held dangerous materials.