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.

“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.