Summers spent building sandcastles on the beach could be a distant memory by the end of the century.
Climate change is changing the face of the British coastline, eroding beaches and marshes.
Conservationists warn that if nothing is done, holiday beaches may be lost within 100 years along with habitat that shelters wildlife.
Many beaches are disappearing
International experts are meeting in London on Wednesday to discuss ways to protect the UK's coastal assets.
It depends on working with nature rather than against it, say experts from "Living with the Sea", a four-year European partnership headed by English Nature.
"For many centuries we've over-engineered our coast and now in the face of unstoppable sea level rise we have to think of all coastal management options," says Stephen Worrall of Living with the Sea.
"We have to work with nature and not fight nature on the coast.
"It means allowing the sea back into some of the undeveloped frontages such as farmland."
Living with the Sea says a rise in sea levels driven by climate change has already altered the coastal landscape around the UK. (The south of England is of particular concern because it has been gradually sinking compared with the north since the last ice age.)
Resorts like Weymouth in Dorset have been robbed of sand while vast tracts of salt marsh have disappeared in counties such as Essex.
It appears that concrete and steel defences put up to protect land from erosion and flooding are putting beaches and other marine environments under pressure.
Beaches have changed over the years
Sand dunes and marshes naturally shift inland as sea levels rise but are unable to do so if they meet a hard barrier.
These "hard-engineering" solutions could radically change the appearance of beaches for future generations, impoverishing coastal wildlife, says the partnership (which also includes the Environment Agency and the Department for Environment, Food and Rural Affairs).
The habitat of the two million water birds that spend the winter in the UK is at risk, says the Royal Society for the Protection of Birds (RSPB).
"There will come a time when if you don't give way to the sea you will be left with a huge problem," says spokesman Grahame Madge.
"You have to recreate these habitats inland if you're to protect them."
The RSPB says it is possible to restore inter-tidal habitat by resetting sea defences, as a pilot scheme at Freiston Shore Nature Reserve in Lincolnshire has shown.
A flood defence was erected inland and the sea was allowed to breach the original sea wall, allowing birds and other wildlife to thrive.