Concern as River Teme in Shropshire contaminated
Traces of neonicotinoids were found in the waters of the River Teme in south Shropshire.
Neonicotinoids were banned from use on flowering crops in the European Union in 2013 due to the harm they cause to bees and other vital pollinators.
Evidence is growing that neonicotinoids harm other species, such as songbirds.
Of the 23 rivers tested across Britain, neonicotinoids were not detected in six.
No official limits exist in the EU for neonicotinoid pollution in freshwater.
Like flying insects, aquatic insects are vulnerable to neonicotinoids and provide the main source of food for many fish and birds.
John Hughes from Shropshire Wildlife Trust said he was not surprised that trace levels of neonicotinoids had been found in the Teme.
But he said it was hard to determine the effects these pollutants would have on local fish stocks, insects and wildlife.
A new Greenpeace study suggests neonicotinoids are frequently found in waterways close to greenhouses where they have been used.
Arlin Rickard, CEO of the Rivers Trust, said: “We work closely with farmers and growers to reduce and better target chemical and fertiliser usage, however some chemicals are just too damaging and persistent to be tolerated.”