River mouths often act like a 'vacuum' that sucks plastic out of the ocean and pulls it back into the rivers.
March 24, 2026
Original Paper
Temporal variations in net plastic transport from the Rhine and Saigon rivers into the sea
SSRN · 6461214
The Takeaway
We usually think of rivers as conveyor belts carrying plastic out to sea. This study of the Rhine and Saigon rivers found that tidal dynamics often create a 'negative delivery ratio,' where the net transport of plastic is actually upstream, meaning the ocean is frequently dumping plastic back into the river system.
From the abstract
Estuaries are the transition zones between rivers and the ocean, and act as final buffer zones for plastic pollution before entering the sea. Plastic transport and retention in estuaries are the result of a complex interplay between tidal dynamics, freshwater discharge, and estuary characteristics. Despite its importance, net plastic transport between rivers and the sea is poorly understood and quantified. Here, we show that the net plastic transport in estuaries is highly variable over time and