In the second part of our series on the problem of plastics in the world’s oceans, we look at which rivers are emitting the plastic pollution to our oceans.

This series is based upon articles and data presented by Hannah Ritchie a Senior Researcher and Head of Research at Our World In Data. These articles would not be possible with their hardworking and generous sharing policies.

What Rivers Bring Plastics To The Oceans?

To tackle plastic pollution we need to know what rivers these plastics are coming from. It also helps if we understand why these rivers emit so much.

Most of the world’s largest emitting rivers are in Asia, with some also in East Africa and the Caribbean. In the chart we see the ten largest contributors. This is shown as each river’s share of the global total. You can explore the data on the top 50 rivers using the +Add river button on the chart.

Seven of the top ten rivers are in the Philippines. Two are in India, and one in Malaysia. The Pasig River in the Philippines alone accounts for 6.4% of global river plastics. This paints a very different picture to earlier studies where it was Asia’s largest rivers – the Yangtze, Xi, and Huangpu rivers in China, and Ganges in India – that were dominant.

What are the characteristics of the largest emitting rivers?

First, plastic pollution is dominant where the local waste management practices are poor. This means there is a large amount of mismanaged plastic waste that can enter rivers and the ocean in the first place. This makes clear that improving waste management is essential if we’re to tackle plastic pollution. Second, the largest emitters tend to have cities nearby: this means there are a lot of paved surfaces where both water and plastic can drain into river outlets. Cities such as Jakarta in Indonesia and Manila in the Philippines are drained by relatively small rivers but account for a large share of plastic emissions. Third, the river basins had high precipitation rates (meaning plastics washed into rivers, and the flow rate of rivers to the ocean was high). Fourth, distance matters: the largest emitting rivers had cities nearby and were also very close to the coast.

The authors of the study illustrate the importance of the additional climate, basin terrain, and proximity factors with a real-life example. The Ciliwung River basin in Java is 275 times smaller than the Rhine river basin in Europe and generates 75% less plastic waste. Yet it emits 100 times as much plastic to the ocean each year (200 to 300 tonnes versus only 3 to 5 tonnes).⁷ The Ciliwung River emits much more plastic to the ocean, despite being much smaller because the basin’s waste is generated very close to the river (meaning the plastic gets into the river network in the first place) and the river network is also much closer to the ocean. It also gets much more rainfall meaning the plastic waste is more easily transported than in the Rhine basin.

If you want to explore the plastic inputs from each of the world’s rivers, the Ocean Cleanup Project provides a beautiful interactive map where you can see this in more detail.