A new study shows that 86 per cent of the world's rivers have been damaged by human activity. The study was conducted by researchers from a university in Toulouse, France. They examined data on over 2,500 rivers around the world. They did not look at rivers in the polar regions of the Arctic and Antarctica or in deserts. The scientists looked into changes to biodiversity over the past 200 years. They discovered that biodiversity in over half of rivers has been seriously damaged by humans. The researchers said there were many reasons for this damage. A big reason is the introduction of new species of fish into rivers. Other reasons include pollution, dams, overfishing, farming and climate change.
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The researchers say the worst-hit rivers are in western Europe and North America. This is because these regions have large and rich towns and cities. The lead researcher said: "Rivers which have the most economic development around them, like the Mississippi River, are the most strongly impacted." The River Thames in London was one of the worst-affected rivers in the study. The least-impacted rivers are in Africa and Australia. The researcher said: "This is probably due to a slower rate of industrialisation in Africa and low population density around rivers in Australia." He added that rivers in many rich nations are unrecognisable compared with how they were 200 years ago.