Rivers are of particular interest because they represent the primary mechanism by which inland plastic finds it's way into the ocean. Coastal releases of plas

Rivers are of particular interest because they represent the primary mechanism by which inland plastic finds it's way into the ocean. Coastal releases of plastic only happen in coastal regions. Granted, most of the world's population lives reasonably close to a coast, but even in those regions the plastic waste is often carried to the ocean by water through smaller waterways, such as rain water carrying plastic litter down storm drains. (Or the waste is left directly on the beach and the next high tide picks it up.) This article goes into the correlation between plastic waste in Asian rivers and Monsoon season: https://www.nature.com/articles/ncomms15611 https://www.nature.com/articles/ncomms15611 That correlation suggests that a large portion of plastic in Asian rivers is being carried into those rivers by rain water, a similar mechanism to how plastic waste is emitted from coastal regions. Of course there are other mechanisms in play too, such as municipalities deliberately, perhaps illegally, dumping their waste into rivers or off a coast. But a ton of it is coming from ground litter either left directly on the beach or carried to the ocean one way or another by water. Regions with the heaviest rain and the most ground liter are the biggest contributors, as you would logically expect.