Pesticides, antibiotics, animal medicines: the chemical cocktail seeping into our rivers

A study of Yorkshire's rivers is helping scientists understand the impact everyday pollutants are having on waterways - and the results are sobering

• Photographs by Christopher Thomond

Rivers carry more than just water through Britain's landscapes. A hidden cocktail of chemicals seeps out of farmland, passes undetected through sewage treatment works, and drains off the roads into the country's rivers. Normally these chemicals flow through unreported, silently restructuring ecosystems as they go, but now, UK scientists are building a map of what lies within - and the damage it may be causing.

Trailing down the centre of Britain is one river whose chemical makeup scientists know better than any other. The Foss threads its way through North Yorkshire's forestry plantations, patchworked arable land and small hamlets, before descending into the city of York, passing roads and car parks, gardens replacing farmland. Along the course of its 20-mile (32km) length, the chemical fingerprints of modern life accumulate.