Plastic is one of the best materials ever invented, but it doesn’t belong in the ocean. Large pieces of it can entangle turtles, birds, sharks, and other marine animals. Tiny bits of plastic, the result of the degrading actions of waves and sun, can linger for decades; once they get into the food chain, they, too, can adversely affect marine life. Many scientists and concerned citizens alike think that humankind should try to clean up oceanic plastic. But before we can best start the process, we need to understand how plastic moves through the ocean.