Almost 500 different chemicals, some of which are banned, have been found in various mixtures across all 171 river and groundwater catchments tested in England in 2024, according to data from the Environment Agency, analysed by the Guardian and Watershed Investigations.

More than half of them are classified as very toxic, toxic or harmful to aquatic life, according to the European Chemicals Agency (ECHA), and a banned, carcinogenic “forever chemical” was among 20 “substances of very high concern” found.

“What this shows is that the way we monitor and manage chemicals in our rivers is completely unfit for purpose,” said Alistair Boxall, professor in environmental science at the University of York.

“Although it depends on the concentrations, a lot of these are very toxic. We know they target algae, invertebrates and fish. If you’ve got a mixture of a few hundred substances, they are potentially working together and exacerbating the effect,” explained Boxall.

Environmental groups have called chemical pollution the silent killer in our waterways. The world has lost 83% of its freshwater aquatic life in 50 years and in UK waters, the sturgeon and the burbot have vanished and Atlantic salmon is endangered.

“Our invertebrate monitoring shows clear evidence of significant chemical impact across all the 100-plus rivers we monitor,” said the WildFish CEO, Nick Measham. “It ties together chemical presence with widespread ecological impact. It makes poo in rivers look like a second-order problem.”

Neonicotinoid pesticides are banned in the UK and EU for use on all outdoor crops because of the high risk to pollinators. However, the data shows all three banned neonics across 29 river and groundwater catchments, including thiamethoxam, which the UK government has continued to allow for sugar beet crops. The Environment Agency said policies were being changed to prevent this use.

Another neonic, imidacloprid, is still legally used as a flea treatment for dogs and cats, which experts say is nonsensical.

“Imidacloprid is like novichok for insects,” said Dave Goulson, professor of biology at Sussex University.

“A single teaspoon of this pesticide is enough to deliver a lethal dose to 1.25 billion honey bees. It’s concerning that our rivers should be awash with a potent insecticide.”

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