Substances also known as biocides have been found in the Wensum, Waveney, Yare and Stiffkey, along with the man-made Cut-Off Channel, in the west of the county.

A study by the Wildlife and Countryside Link and Rivers Trust says at least one of a list of six harmful chemicals was found in 95pc of waterways tested by the Environment Agency (EA).

The findings will raise fears over the impact on wildlife as well as those who swim in the rivers.

The chemicals detected included traces of substances used in disinfectants, cleaning products, insecticides, rat poisons, wood preservatives, glues, carpets and furniture, paints and paper products.

It comes as campaigners accuse the government of trying to water down consumer and environmental protection protocols agreed by European Union countries after Brexit.

All six chemicals were found in the River Wensum in Norwich and the Waveney at Ellingham Mill, near Beccles.

Boats on the Wensum, near the centre of Norwich (Image: Antony Kelly) Five were found in the Yare at Buckenham Ferry, four in the Cut-Off Channel near Downham Market, and two in the Stiffkey at Wighton Bridge.

Dr Rob Collins, director of policy and science at........

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