Sea turtles can confuse plastic bags for jellyfish. A turtle in the water can’t tell the difference and will often eat the bag, which gets stuck in their stomach.
Trash on nesting beaches. Adult sea turtles in many places need to crawl through collected debris to find a place to nest and hatchlings can get caught in the debris trying to make their way to the ocean. Tiny bits of plastic in the sand can also affect nests and hatchlings.
They can get stuck in it while swimming. Many turtles make long migrations and pass through areas with a lot of ocean plastic. They can get caught in things like six pack rings or discarded fishing gear.
Mylar balloons filled with helium can also look like jellyfish. These balloons can travel hundreds of miles in the air and land in rivers or the ocean.
They can consume micro plastic from their food. Tiny bits of plastic consumed by fish or other animals can then be eaten by those who eat them, like turtles (and humans.)