They think the ocean is big and can hold a lot of sewage. Many countries treat the ocean like a watery garbage dump. Animal sewage also gets into the ocean. Sometimes rain washes manure into a stream that runs into the ocean. Sometimes it runs into ditches that lead to the ocean.
Most farmers use chemicals to kill bugs and grow crops.
When it rains, these chemicals can wash out of the plants and soil. From there it runs into ditches or streams. If this drains into the ocean, it is called run-off. This can be as bad for the turtles as sewage is. Turtle scientists are finding many sick turtles around places where there are sewage and run-off problems.