Unesco has sent out a message on Earth Day 2018, calling for an end to plastic pollution at heritage'>World heritage sites.

Research suggests that rubbish and pollution are a significant problem at many World Heritage sites. Increased tourism means that more people are leaving trash at the world’s most iconic sites.

Marine pollution is also a problem, with waste including plastics washing up on beaches. Unesco says that birds, turtles and marine mammals get entangled in marine litter or mistake it for food, leading to high mortality rates.

"We must stop using so much plastic, and dispose of waste properly at sites, using trash bins or taking rubbish away with us, to dispose of it properly," said Unesco.

"Part of the problem for marine sites is the natural ocean currents that bring waste to rest on certain beaches, so it’s important to reduce waste overall."

Several World Heritage sites have created clean-up and awareness programmes, which serve as a model for protected areas around the world. These include the remote Papahanaumokuakea atoll in Hawaii, which has had almost 1,000 tons of marine debris has removed from its shores since 1996. The iSimangaliso Wetland Park also has regular clean-ups and awareness programs to protect the beaches along its 220km of coastline. By contrast, the UK overseas territory of Henderson Island struggles with sea debris, with the highest recorded density anywhere in the world.

"We must take action," said Unesco. "Cleaning up is just a start – we also need to use less plastic and not put waste in our oceans. Let’s keep our beaches clean, and dispose of plastics properly or not use them at all. The future of our oceans depends on it."