More than 100 dead and dying turtles have been washed up on beaches in the South American country El Salvador.
Experts are baffled as to why the rare animals are dying and fear another 600 could perish in the next few days.
Specialist Dr Carlos Drews said this could be one of the worst calamities to hit the 2,000 turtles that live there.
The dead turtles are from three different species, all of which are endangered: olive ridleys, hawksbills and black sea turtles.
It had been thought that the turtles had been killed in fishing nets or by a massive growth of algae, called a red tide, which had polluted the waters.
But marine biologists are continuing to investigate the deaths and think they could also be due to a kind of bacterial infection.
Dr Drews said: "The international conservation community is watching this and is very worried."