Warm water caused by El Nino is being suspected of bleaching around one quarter of coral reefs off Vietnam's famous resort island Con Dao, making them vulnerable to a massive die-off, local media reported on Friday.
The bleaching started in March and has affected around 400-500 hectares of coral reefs, the Vietnam News Agency said, citing the management board of Con Dao National Park.
The report did not mention if human activities were also to blame.
Con Dao, about 97 sea miles off the popular beach town of Vung Tau, is one of the favorite diving destinations in Vietnam.
Corals are often bleached when warm water causes them to expel the algae living in their tissues. While they can still survive the bleaching, they will die when the algae loss prolongs.
At least eight coral reefs areas for have been hit by bleaching such as those around the Con Son Bay and Tai Island, according to the management board.
Con Dao reported coral bleaching in 1998 and 2010, according to the news report.