Record of Thames water tests
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Long rise in Thames nitrate pollution

Scientists have assembled a remarkable record of water quality in the Thames that stretches back over 140 years.

The archive is thought to be the longest for any river in the world.

Putting it together involved hunting down old paper documents detailing monthly water tests. Some of them even had to be retrieved from America.

Durham University's Dr Fred Worrall told our correspondent Jonathan Amos what the record shows.