Just 10 Rivers Contribute Up to 95% of River-Based Ocean Pollution

ENVIRONMENT

Just 10 rivers may be responsible for dumping almost four million tonnes of plastic into the ocean every year. (Cosmos)

Use our activity to help students trace the sources and impacts of marine debris.

Teachers, scroll down for a quick list of key resources in our Teachers Toolkit, including today’s great MapMaker Interactive map.

Children collect and recycle garbage below the Old Iron Bridge on the polluted Yamuna river in Delhi, India. The Yamuna is the longest tributary of the Ganges, which contributes tons of plastic pollution to the ocean every year.
Photograph by Matthieu Paley, National Geographic

Use today’s MapMaker Interactive map to discuss why these 10 rivers contribute so disproportionately to riverine pollution of the ocean.

Discussion Ideas

Before reading the Cosmos article, read through our terrific activity “Marine Debris: A Legacy of Litter.” What is marine debris? You can also read through our reference resource for some help.
- Marine debris simply describes any garbage, refuse, or other objects that enter the coastal or ocean environment. Marine debris may include lost fishing nets, medical waste, cigarette butts, and, perhaps most importantly, plastics.
  - The term “marine debris” generally does not include chemical pollution such as runoff.

What is the source of most marine debris? Read through the short Cosmos article for some help.
- land-based activity. According to Cosmos, previous research estimated that about 80% of marine debris comes from land, between 4.8 million and 12.7 million tonnes a year. Most plastic debris comes from coastal cities and towns, where litter is washed into storm drains and flows into the sea. However, plastic debris from inland watersheds also contributes to land-based pollution. Watershed debris can be transported to the ocean through beach litter, storm drains, canals, unlined landfills, and rivers. Learn more about watersheds with our activity here.
- ocean-based activity. The remaining 20% of marine debris “comes from marine activities – plastic tossed from fishing boats, ships, drilling platforms and so on.”

The new study analyzes the sources of “MMPW” in the world’s rivers that end up in the ocean. What is MMPW?
- MMPW is mismanaged plastic waste. MMPW includes “material that is either littered or inadequately disposed. Inadequately disposed waste is not formally managed and includes disposal in dumps or open, uncontrolled landfills, where it is not fully contained. Mismanaged waste could eventually enter the ocean via inland waterways, wastewater outflows, and transport by wind or tides.”
  - MMPW includes both microplastics and macroplastics. Microplastics are less than 5 millimeters (.19 inches) in diameter, while macroplastics are larger.

Some alarming headlines about this study claim that “95% of plastic polluting the world’s oceans comes from just ten rivers.” Is this what the research actually says?
- No. Research indicates that ten rivers contribute between 88% and 95% of plastic pollution from rivers. Most plastic pollution comes from coastal cities and towns.

Use today’s MapMaker Interactive map to discuss why these 10 rivers contribute so disproportionately to riverine pollution of the ocean. Use the bookmarks to consider how population density and land-use patterns may impact river pollution.

Take a look at today’s MapMaker Interactive map. Why do you think these ten rivers account for such a huge proportion of river-based plastic marine debris?
- size. One of the researchers says “large rivers are particularly efficient in transporting plastic debris. Large rivers like the Yangtze transport a higher fraction of the MMPW that is generated in their catchments than smaller rivers.”
- population density. “[R]ivers with the highest estimated plastic loads are characterised by high population – for instance the Yangtze with over half a billion people.”
- location. Many of these big rivers flow through different municipalities, states or provinces, and nations. In fact, some the rivers serve as borders between nations. (At various points, for instance, the Mekong forms the border of China, Myanmar, Laos, Thailand, and Cambodia.) Each municipality, state, or nation may have different environmental regulations and policies regarding the river. Downstream nations often have less control over the streamflow than upstream nations. (This has huge political implications that stretch into environmental, industrial, and health-care policies. Learn more about river management policies on the Nile with this study guide.)
- economics. All of the most-polluting rivers flow through nations with rapidly developing economies, including China and India. Economic development programs may include a focus on agricultural and industrial infrastructure. Strict environmental policies aren’t always a part of economic development programs, and this is not just true for developing economies.