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