Record of Thames water quality
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Scientists trace Thames nitrate rise

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.

Bristol University's Dr Nicholas Howden told our correspondent Jonathan Amos what information was held in the record.