The southern Mexico Mayan ruins of Calakmul have become the country's first site to receive the "mixed" World Heritage designation from the United Nations.
The designation cites both the pyramids of the ancient city-state and hundreds of thousands of acres of well-preserved tropical forest that surrounds them.
But authorities say the heritage designation for another Mexican site, the "floating gardens" of Xochimilco, could be in danger.
The man-made islands created by the Aztecs have been hit by pollution and urban sprawl, endangering the endemic salamanders known as axolotls.
The director of the country's National Institute of Anthropology and History says there is a plan to rescue Xochimilco.
But Teresa Franco said Wednesday that it could be at risk "if quick and efficient action isn't taken."
Explore further: Builders bulldoze big Mayan pyramid in Belize (Update 2)