The Taj Mahal will collapse within five years unless urgent action is taken to fix its rotting foundations, campaigners warn.
The 358-year-old marble mausoleum is India's most famous tourist attraction, bringing four million visitors a year to the northern city of Agra.
But the river crucial to its survival is being blighted by pollution, industry and deforestation.
Campaigners believe the foundations have become brittle and are disintegrating.
Cracks appeared last year in parts of the tomb, and the four minarets, which surround the monument, are showing signs of tilting.
The Taj Mahal was built by Mogul emperor Shah Jahan, who was grief-stricken by the death of his wife Mumtaz Mahal in childbirth.
A campaign group of historians, environmentalists and politicians say time is running out to prevent a ''''looming crisis''''.
"If the crisis is not tackled on a war-footing, the Taj Mahal will cave in between two and five years," the Daily Mail quoted Ramshankar Katheria, the MP for Agra who is leading the campaign, as saying.
"The architectural wonder of the world is losing its shine, and if this persists the minarets may also collapse since the wooden foundation - beneath the wells - is rotting due to lack of water.
"No one has been allowed to go into the foundations for the last three decades. If everything is fine, what have they got to hide?"
Professor Ram Nath, a historian who is one of the world's leading authorities on the Taj, said: "The Taj stands just on the edge of the river Yamuna which has now dried up.
"This was never anticipated by its builders. The river is a constituent of its architectural design and if the river dies, the Taj cannot survive," he added.