You can read this frequently, but this claim is probably false. It misquotes the results of research published in 2017. In that study, scientists estimated how much plastic enters the sea from rivers around the world. Ten of these river systems carried most of the plastic. But plastic also reaches the sea through other ways, not just rivers. So the total amount of plastic entering the ocean is higher than just this riverine input. And new research suggests that a much larger number of rivers are involved in carrying plastics to the sea.