Plastic gets into the ocean in many ways. It is dumped directly or is blown in by the wind. It comes from ships and lost fishing gear. It is also carried by rivers. One estimate of total plastic input to the oceans from all sources is around 8 million tonnes per year, and about 80% is attributed to land based-sources. However, it’s not possible at this stage to accurately verify these figures.
In a recent study of the amount of plastic litter transported by 57 river systems, 10 rivers were estimated to be responsible for 90% of it. In other words, 90% of the plastic coming from rivers is from these 10. It does not mean that 90% of all plastic in the ocean is coming from these 10 rivers. Although there is a great degree of uncertainty with this estimate (ranging from 04. To 4 million tonnes per year), it is a good indicator of the importance of rivers as a source of marine litter. It also helps target regions where better waste management practices are needed.
So, while river-borne plastics are undoubtedly a major source of marine litter, the data is still limited and we should not ignore marine pollution from other sources. One thing we do know is that the presence of plastics in our ocean is linked to human activity – on land and at sea. “All sectors and individuals contribute to this pollution – from poorly controlled waste sites, illegal dumping and mishandled waste on land to ropes, nets, floats and other debris from fishing, merchant shipping, oil rigs, cruise ships and other sources”.
River-borne plastics are an important source of marine littler and while research continues into which sources are the most important, we know that plastic in the ocean is a global problem. And it is clear that action by all of us – from individuals to governments – is required to tackle it.
 Jambeck, J.R. et al., 2015. Plastic waste inputs from land into the ocean Science, 347(6223), pp. 768-771 (DOI: 10.1126/science.1260352) Available at here
 Schmidt, C. et al., 2017. Export of Plastic Debris by Rivers into the Sea. Environ. Sci. Technol., 2017, 51 (21), pp 12246–12253 (Available here).
Stemming the Plastic Tide: 10 Rivers Contribute Most of the Plastic in the Oceans
 UNEP, 2016. Marine plastic debris and microplastics – Global lessons and research to inspire action and guide policy change. United Nations Environment Programme, Nairobi.
UNEP and GRID-Arendal, 2016. Marine Litter Vital Graphics. United Nations Environment Programme and GRID-Arendal. Nairobi and Arendal. www.unep.org, www.grida.no