There’s too much plastic in our ocean. But where does it come from? Where does it do most harm? And what can we do about it? 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 around for decades; once they get into the food chain, they too can adversely affect marine life. Many of us — scientists and concerned citizens alike — think that humankind should try to clean up oceanic plastic. But before we can best start the cleanup, we need to understand how the plastic moves through the ocean.