With chants from Buddhist monks and a flotilla of ceremonial flowers behind them, the reptiles inched into the Sre Ambel river system, in southwestern Preah Sihanouk province.
Conservationists hope they will form new breeding populations.
Cambodia is home to several populations of endangered turtles, coveted as delicacies and traditional medicine in Vietnam and China.
Royal Turtles -- formally classified as Southern River Terrapins -- have been pushed to the brink of extinction by hunting and sand mining, which destroyed the banks where they lay their eggs.
The damage was so severe that in 2000 they were feared wiped out in Cambodia, before nests were found and a careful conservation effort began.
"Our team raised them since they hatched until now... these turtles are 12 or 13 years old," Som Sitha, technical advisor to the Wildlife Conservation Society, which ran the scheme with the help of EU funds.
"We are releasing them to restore their numbers in nature. We hope that these turtles will breed in the near future," he said, urging local communities to help protect them.
Source: AFP