A green turtle that washed up dead on a beach in Cyprus was found with 183 pieces of plastic in its gastrointestinal tract.
The sea creature was one of 34 turtles examined in the same area by scientists from the University of Exeter and the Society for the Protection of Turtles.
Scientists said the animals are being fooled by plastic that looks like their natural diet.
The unsuspecting creatures are more likely to swallow plastics that resemble sea grass, potentially from sources like bin bags, as well as fragments of fishing rope and carrier bags.
One small green turtle was found to have ingested 183 pieces of plastic, including a balloon.
Dr Emily Duncan, of the University of Exeter, said: “Previous research has suggested leatherback turtles eat plastic that resembles their jellyfish prey, and we wanted to know whether a similar thing might be happening with green turtles.
“Sea turtles are primarily visual predators – able to choose foods by size and shape – and in this study we found strong evidence that green turtles favour plastic of certain sizes, shapes and colours.
“Compared to a baseline of plastic debris on beaches, the plastic we found in these turtles suggests they favour threads and sheets that are black, clear or green.”
Researchers could not determine what, if any, role the plastic had in the turtles’ deaths.
The majority of the 34 turtles examined had most likely died as a result of getting tangled in fishing nets, they said.
Turtles containing the most plastic were smaller in size, possibly because they are less experienced and more likely to eat the wrong food, scientists said.
The study published in the journal Scientific Reports said this could also be due to diet choices evolving with age and size.
Out of the 34 turtles looked at, the full gastrointestinal tracts of 19 were examined.
All of the turtles were found to have ingested plastic, with the number of pieces ranging from three to 183.
Professor Brendan Godley, who leads the Exeter Marine research strategy, said: “Research like this helps us understand what sea turtles are eating, and whether certain kinds of plastic are being ingested more than others.
“It’s important to know what kinds of plastic might be a particular problem, as well as highlighting issues that can help motivate people to continue to work on reducing overall plastic consumption and pollution.”