Does Plastic Pollution in the Oceans come from Rivers?

Two different claims:

- 95% Of Global Plastic Waste In Oceans Comes From Just TEN Rivers In Asia & Africa.

- Stemming the Plastic Tide: 10 Rivers Contribute Most of the Plastic in the Oceans (Scientific American)

- 90% of plastic polluting our oceans comes from just 10 rivers

- Almost all plastic in the ocean comes from just 10 rivers

- Shocking report reveals that 95% of plastic polluting the world's oceans comes from just TEN rivers including the Ganges and Niger

- Just 10 river systems transport more than 90% of all plastic waste to the world’s seas, new research shows

A couple had a slightly different claim:

- JUST 10 RIVERS CONTRIBUTE UP TO 95% OF RIVER-BASED OCEAN POLLUTION

- Just 10 streams carry 95% of all river-borne plastic into the ocean

The discrepancy isn't that some articles say 90% and some say 95% (the paper says it's around 90%). The difference between the claims is that some say X% of river based plastic pollution, and the others say X% of all plastic pollution.

The difference is really important. If we're talking about all plastic pollution then we can focus our efforts on these 10 rivers and pretty much eliminate the plastic pollution problem. It also means most of our efforts outside of these areas are mostly in vain.

On the other hand, if these 10 rivers are taken out of only river based pollution and river based pollution is a relatively low percent of total plastic pollution, then it really doesn't matter that much.

First of all, the paper is clearly talking about river based plastic pollution. Most of the reporting got it wrong. But whether it's important will depend on how much ocean pollution comes from rivers.

The National Geographic article is the only one that mentions this issue. It says that most plastic pollution comes from coastal cities and towns, not rivers. It is National Geographic, an organization I'm hardly skeptical of, and they state it quite confidently, but I would still feel more comfortable with a stronger source.

So I found MarineLitterFacts, who say that 80% of ocean plastic comes from land-based sources, the other 20% are water based. This sounds like rivers are not a significant contributor to ocean plastic pollution.

But as it turns out, rivers are classified as land-based sources. Somebody needs to tell these people that rivers are made of water.

A little more digging and I found this paper in Nature. It estimates that between 2.8–18.6% of plastic emissions occur via river transport. Confirmation at last. Like many of the sources I peered at, it emphasized how imperfect these estimates are. Okay, we're being cautious. But it's not like next week the estimates are going to be 80%.

I think this basically affirms my suspicion that a lot of reporting on the issue gives a very wrong impression. If only 18% of plastic in the ocean comes from rivers, then the highly reported 90% is only out of that 18%. We can't just focus our efforts on these rivers to fix our problems.