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The worst-hit rivers are in
Europe and North America. These
have big, rich towns and cities. The lead researcher said: "Rivers which have the most
development around
, like the Mississippi River, are the most
impacted." London's River Thames is one of the worst-affected in the
. The least-impacted rivers are in Africa and Australia. The researcher said this is because of less
in Africa and low populations around rivers in Australia. He said rivers in
nations are completely different to
they were 200 years
.
