Unesco has declared Madagascar's tropical forest and the Everglades National Park in the United States to be endangered world heritage sites.
At the same time it has removed the Galapagos Islands from the at-risk list, saying Ecuador has made significant progress protecting the islands' ecosystem.
The UN agency says agricultural and urban development in Florida's Everglades have reduced water flow in the wetland - a sanctuary to many birds and reptiles - by 60%. The pollution level there is so high it's killing marine life, Unesco adds.
It is the second time the Everglades have been added, the BBC reports. They were first classified as at-risk between 1993 and 2007 after being devastated by Hurricane Andrew.
"We commend the USA's request to re-inscribe the site on the danger list, and its plans for major infrastructure overhaul to restore the Everglades' fragile wetland ecosystem," says Mariam Kenza Ali of the International Union for Conservation of Nature (IUCN).
Call for halt to illegal logging
The Atsinanana rainforests of Madagascar, which lie within six national parks in the east of the island, were put on the list because of the threat to the many unique species inhabiting them, especially primates and lemurs.
"In adding this site to the danger list, we are calling for international action to halt illegal logging and to also ensure that no illegally logged precious woods from Madagascar enter national markets," says Tim Badman, head of World Heritage at the IUCN.