(CNN) — With its dramatic volcanic landscape, whitewashed cottages and blue-domed churches, the picturesque Greek island of Santorini is never short of tourists.
Many travel by boat before making their way up hundreds of steep steps to the island's main town, with donkeys available to carry those who can't or don't want to walk.
But the donkeys have been taking too much of the strain, say activists who have launched a campaign to make visitors think twice before they hop on.
British charity The Donkey Sanctuary has launched the "In Their Hooves" campaign as a way of improving public awareness of the animals' health.
It says the strain of carrying overweight tourists is injuring the donkeys' spines.
In October last year, the Greek government banned tourists weighing more than 100 kilograms (220 pounds) from riding the animals, but "In Their Hooves" is an attempt to make all visitors think twice about riding working animals.
Visitors are asked to consider whether the animals have adequate water and shelter, if the owner treats them respectfully or if they have any signs of injury, and whether they are expected to carry an acceptable weight.
The initiative, which includes a campaign video, is the result of a partnership between The Donkey Sanctuary and local authorities in Santorini.
"We are excited to launch the In Their Hooves video and we hope visitors to Santorini are able to make informed decisions about the welfare of working equines they will see there," Barbara Massa, The Donkey Sanctuary's regional director for Europe, said in a press release.
"We will continue to work with the municipality, providing training to equine health service providers and also the animal owners, all of whom are critical to improving the working conditions and practices on the island."
Santorini is a popular stop on Mediterranean cruises, and "In Their Hooves" is supported by the Cruise Lines International Association (CLIA), an industry body.
CLIA members will show the campaign video to passengers, the press release said.
"Over recent years we have had several complaints from cruise passengers about the way donkeys were being treated on islands such as Santorini: for example, where rides are offered on donkeys and mules that have been tethered for hours on end in the hot sun unable to access water," said Tom Boardley, secretary general at CLIA Europe.
"We fully support The Donkey Sanctuary's In Their Hooves Campaign and hope it will go some way to reassure our passengers that we care about animal welfare in destinations on our members' cruises."
And it's not just Santorini's donkeys that are struggling to cope with mass tourism.
In 2017, the island's authorities imposed a daily limit of 8,000 cruise ship passengers, after as many as 18,000 people a day visited the island in 2016.
Locals also worry about the environmental effects of a hotel-building spree that saw water use skyrocket.
However a recent boom in wine-making, encouraged by incentives from the European Union, has slowed the pace of construction in favor of maintaining vineyards.