Conservation International says the unsustainable taking of turtles for food and to supply a lucrative pet trade are behind the drop in numbers of the estimated 280 world species, the BBC reported Friday.
Turtles are highly sought in Asia, particularly in China, where turtle meat is believed to have medicinal benefits.
Habitat loss caused by damming of rivers for hydro-electricity is another major problem, CI said.
The outlook is worrisome, said Peter Paul van Dijk, director of CI's Tortoise and Freshwater Turtle Conservation Program.
"These are animals that take 15-20 years to reach maturity and then live for another 30-40 years, putting a clutch of eggs in the ground every year," he said.
"They play the odds, hoping that in that 50-year lifetime, some of their hatchlings will somehow evade predators and go on to breed themselves.
"But if you take these animals out before they've reached 15 and can reproduce, it all ends there," van Dijk said.