Tourists on Mamma Mia! island asked: voulez-vous return your pebbles?

Usually at this time of year, Greek beaches are basking in the sunlight of summer’s dying days. But recently the news has been less luminous. First came the terrifying footage, taken by tourists, of a landslide on Zante’s Navagio beach. The collapse of the cliff face only narrowly missed holidaymakers sunbathing on its shores below.

Now comes the news that a bay on Skiathos – the island that served, partially, as a backdrop for the first Mamma Mia! film – is losing its smooth pebbles so fast campaigners have been forced to take drastic action.

This week containers emblazoned with the words “Lalaria Beach return pebbles box” appeared at Skiathos’s airport as locals stepped up the campaign to save the beach from tourists who crave one of its famously smooth marble stones. “We’ve had no other choice,” said Thodoris Tzoumas, who heads Skiathos’s cultural association. “Lalaria may not have suffered a landslide but human intervention is such that its natural beauty is being destroyed at an alarming rate.”

Thanks to pebble pinching whole chunks of its stony shoreline have vanished.

The appearance of the honesty boxes follows the announcement of fines up to €1,000 (£894) for tourists found in possession of Lalaria’s celebrated marble stones. Posters have also been pasted on local cruise boats and a billboard placed on the beach exhorting holidaymakers to “take a picture not a pebble”.

“Lalaria is not a protected site so the fines were announced in extremis,” the island’s harbour master chief, Nikolaos Katsambas, told the Guardian. “Now that all these measures have been taken we hope they will have a deterrent effect.”

Campaigners claim the marbles have been disappearing at an alarming rate. Lalaria, on Skiathos’s northern coast, first became famous in the 1970s when the Greek tourist board, attracted by its crystal clear waters, made the bay the country’s poster beach. It shot to global stardom, however, when Hollywood producers used Skiathos as one of the film locations for the first Mamma Mia. This summer’s release of Mamma Mia! Here We Go Again has lured even greater numbers of tourists, with many visiting the island to get married or renew vows.

A spokeswoman at the local town hall said tourists were not the only culprits. “Residents here have also been taking them to build fancy walls in their gardens and mosaic floors in their homes,” lamented Athina Papageorgiou. “Nature can’t keep up with replenishing the disappearing stock.”

According to the island’s cultural association, the larger marbles have almost entirely been eradicated from the beach. “In the past, winds lashing the rocks during the winter months would make up for the losses. But we’ve lost so many over the last decade that that’s no longer enough,” he sighed.

As part of the campaign, coastguard officers have also begun conducting inspections as tourists alight from boats running daily cruises to Lalaria, which is only accessible by sea. “They are down there every day and even boat captains are issuing warnings over loudspeakers,” the campaigner added.

Authorities at Skiathos’s airport have reportedly long complained of the inexplicably large amount of pebbles discovered in travellers’ luggage.

But the appearance of the honesty boxes – following the threat of fines – may be working. “We’ve been pleasantly surprised at the result,” said Tzoumas. “They have only been there a few days and they are beginning to fill up. It’s the last chance for pebble thieves to part with these beautiful stones if they don’t want to be found with them.”