About three quarters of the marine litter in the world’s seas is plastic. Research published in 2015 suggests that 4.8 to 12.7 million tonnes of plastic, or 2 to 5 % of plastic waste generated, enters the oceans each year. It is estimated that much of the plastic debris in the ocean is out of sight. Research published in 2018 notes that single-use plastics are widely found even at depths over 6 000 m and have reached the world’s deepest ocean trench.
On European beaches, the European Commission estimates that plastics make up 80–85 % of marine litter by count, and that single-use plastics account for about half of all marine litter by count. These estimates are consistent with findings from Marine Litter Watch, a European Environment Agency initiative involving citizens, as well as with reports on specific seas. As debris can travel over long distances, the issue of marine litter has a strong transboundary dimension.