Drugs, plastics and flea killer: the unseen threats to UK's rivers

Waterways look cleaner but levels of new pollutants are not being monitored

Beer hasn't been sold in steel cans for decades. The cans Keith Dopson found in Slough's Salt Hill stream would be collectors' items were they in good condition, but they had disintegrated into clumps of rust.

"We filled seven bin bags with rubbish," he says. "Just from the river, not the banks. Plastic bottles and cans, lots of cans. Those steel ones must have been there for ages."