ATHENS • Activists on the Greek island of Skiathos - where parts of Hollywood film Mamma Mia! (2008) were shot - have stepped up a campaign to stop tourists stealing their marble stones.

They advised visitors to take a picture instead of a pebble as a holiday memento.

The white, round pebbles were formed from the rocks surrounding Lalaria Beach on the island, which lies east of the Greek mainland.

Several outdoor scenes in Mamma Mia! were shot on location on Skiathos.

The movie starred Meryl Streep, Amanda Seyfried, Pierce Brosnan and Colin Firth.

Lalaria Beach lies on the island's north coast and is accessible by boat.

Activists say that it has been damaged irreversibly over the past decade and must be protected.

"We have seen that most of these pebbles were taken away and that's because the thousands of tourists used to take the pebbles as souvenirs," said Mr Thodoris Tzoumas of the Cultural Association of Skiathos, which started the campaign.

"We decided to take measures together with the board police of Skiathos."

Mr Tzoumas said fines for those found pocketing rocks range from €400 (S$640) to €1,000, depending on the number of pebbles removed. He added that inspections are also taking place at the island's port.

Signs, reading "take a picture not a pebble - save Lalaria Beach", have been placed in tourists boats carrying out daily excursions, while a sign hung on a rock at the beach states that removing stones is illegal.

The association recently installed a box at the airport's security control area for those who may have regrets for their action. Mr Tzoumas said the response was immediate.

Stones, ranging from small pebbles to bigger stones which would take a chunk out of a tourist's baggage allowance, were promptly put in the transparent plastic box.

"Very soon, (the box) was full of pebbles," he said.

REUTERS