Australian officials are investigating why dozens of turtles have been found on beaches in northern Queensland, many of them ill or dead.
It is thought unseasonably cold weather or the flow of floodwaters into the ocean could be to blame.
Conservationists say the number of turtles being washed up near the city of Townsville is unprecedented.
They are worried there may be many more unreported fatalities along isolated stretches of the coast.
Dozens of dead or stranded turtles have been found near Townsville and on Magnetic Island, a tropical resort popular with holidaymakers.
Carcasses have also been found more than 800km (500 miles) to the south around the port city of Gladstone.
There are various theories why this is happening.
Some researchers believe a category-five cyclone that tore across the Queensland coast earlier this year wiped out many sea-grass beds throughout the Great Barrier Reef, leaving sea turtles with little to eat.
Others blame unusually cold weather.
Scientists say it could take years for damaged sea-grass beds to recover.
The coastal waters of Queensland are important breeding grounds for several species of marine turtles, including the Loggerhead, Hawksbill and Flatback.