Humans have damaged most of the world's rivers. Researchers looked at over 2,500 rivers, but none in the Arctic and Antarctica. Humans have seriously damaged biodiversity in over half of rivers in the past 200 years. Reasons include new species of fish in rivers, pollution, dams and climate change.
The worst rivers are near big cities in Europe and America. These rivers have a lot of factories near them. The least-affected rivers are in Africa and Australia. This is because there are fewer factories in Africa and smaller populations around rivers in Australia. Rivers in rich nations are very different to how they were 200 years ago.