Frequently Asked Questions

Riverine plastic emissions refers to the annual mass of plastic waste transported by rivers into the ocean. The most widely cited global estimate is 0.8 to 2.7 million metric tons per year, from Meijer et al. (2021) published in Science Advances.

This is distinct from total aquatic leakage (all plastic entering water from all pathways, ~22 Mt/yr per OECD) and from plastic already accumulated in the ocean (the cumulative stock from decades of leakage).

Source: Meijer et al. 2021; OECD 2022

More than 1,000 rivers account for 80% of riverine plastic emissions into the ocean. This finding from Meijer et al. (2021) revised earlier estimates that focused on roughly 10 major rivers.

The highest-emitting rivers tend to be in regions with dense populations and limited waste management infrastructure, particularly in South and Southeast Asia and West Africa.

Source: Meijer et al., Science Advances, 2021

Estimated annual riverine plastic emissions range from 0.8 to 2.7 million metric tons per year. This range reflects genuine scientific uncertainty in waste generation data, population distribution models, and river flow measurements.

Riverine emissions are one of several pathways by which plastic enters the ocean. The OECD estimates total plastic leakage to aquatic environments at approximately 22 million tonnes per year when all pathways are included.

Sources: Meijer et al. 2021; OECD Global Plastics Outlook, 2022

Earlier studies (Lebreton et al. 2017, Schmidt et al. 2017) suggested roughly 10 major rivers were responsible for most riverine plastic entering the ocean. This framing was widely cited in media and policy discussions.

Meijer et al. (2021) substantially revised this understanding, showing that plastic emissions are distributed across more than 1,000 rivers worldwide. Many small urban and coastal rivers collectively account for a large share. Focusing only on a few big rivers misses the majority of the problem and can misdirect intervention efforts.

Source: Meijer et al. 2021

Small rivers near coastlines can be highly efficient at transporting plastic to the ocean because waste has a short distance to travel and less opportunity to settle or be intercepted. In densely populated coastal areas, even a short urban waterway can carry substantial plastic loads.

The collective contribution of thousands of small rivers is a major factor in global ocean plastic pollution. This is one of the most important findings from Meijer et al. (2021).

Source: Meijer et al., Science Advances, 2021

Scientists use models that combine geospatial data on waste generation, population distribution, proximity to waterways and coastlines, precipitation patterns, and river network topology. The models estimate how much mismanaged plastic waste is likely to enter river systems and be transported to the ocean.

Field measurements from specific rivers are used to calibrate and validate these models, but the global emission figures are model outputs, not direct measurements of every river.

Source: Meijer et al., Science Advances, 2021

All five major ocean basins receive plastic from rivers:

Pacific Ocean

Receives the highest modeled riverine plastic load, driven by rivers in Southeast and East Asia.

Indian Ocean

Major contributions from South Asian rivers (Ganges, Ulhas, and tributaries).

Atlantic Ocean

Contributions from West African and South American rivers.

Arctic Ocean

Lower absolute volumes but ecologically sensitive.

Southern Ocean

Limited direct riverine input, primarily transported by ocean currents.

Sources: Meijer et al. 2021; UNEP 2021

Riverine plastic emissions refer to the ongoing annual flow of plastic from rivers into the ocean (estimated 0.8–2.7 Mt/yr). Plastic already in the ocean is the accumulated stock from decades of input from all sources: rivers, coastal areas, shipping, and more.

Reducing riverine emissions addresses the ongoing flow; cleaning up the ocean addresses the accumulated stock. Both are important, but they require different strategies.

Sources: Meijer et al. 2021; UNEP, 2021

Several factors drive plastic from land into waterways:

Inadequate waste collection

Uncollected plastic accumulates near rivers and is washed in by rain and wind.

Urban drainage systems

Stormwater channels funnel waste directly into rivers.

Seasonal monsoons and flooding

Heavy rainfall events mobilize accumulated waste from riverbanks and floodplains.

Wind transport

Lightweight plastic is blown into waterways from nearby areas.

Population density

More people near rivers means more waste generation and higher risk of leakage.

Sources: Meijer et al. 2021; UNEP 2021

No. The global estimates are modeled using geospatial data on waste generation, population, precipitation, and river networks. Field measurements from specific rivers are used to calibrate and validate the models, but it is not feasible to directly measure plastic transport in every river worldwide.

The model uncertainty is reflected in the wide range (0.8–2.7 Mt/yr). This should be understood as a confidence interval representing the best available scientific understanding.

Source: Meijer et al. 2021