A serious pesticide pollution has hit the upper River Kennet this week resulting in an almost total wipe-out of the aquatic invertebrates in much of a 15km stretch downstream from Marlborough to Hungerford.
As yet fish populations remain unscathed but there are concerns that there may be residual effects that are still to come. Much of this stretch of famous chalkstream, renowned for its trout fishing, is situated within a SSSI (site of special scientific interest.)
The Environment Agency (EA) has identified the pollutant as chlorpyrifos, an organophosphate that is highly toxic to insect life. The source is as yet unknown but it entered the river by passing through the Marlborough Sewage Treatment Works. No damage appears to have been done to the works themselves. A team of specialists from both Thames Water and the EA are working together on trying to track down the cause and origins of the pollution.
Chlorpyrifos is used on lawns and golf courses and to tackle insects on crops and some soft fruits. It is the same pollutant that wiped out a large section of the River Wey in 2003 and led to a significant fish kill on the Sussex Ouse in 2001.
The US Environmental Protection Agency (EPA) has moved to limit the use of the chemical near salmon rivers because of possible damage to fish and has been petitioned to introduce a total ban following reports that it can cause damage to human health.
The pollution was discovered on Monday by volunteer riverfly monitors working for Action for the River Kennet (ARK). In their statement ARK said: "The Environment Agency were immediately alerted, as well as the downstream river keepers. By this morning the pollution had spread from the Elcot Lane area to beyond Ramsbury, but the river upstream of Elcot was healthy.
"The Environment Agency are currently investigating the extent and cause of the incident. Although few fish appear to have been killed the absence of invertebrates means that both fish and other wildlife have nothing to eat, which will have a serious impact on the river's ecology. ARK have a team of over 50 volunteer riverfly monitors who monitor over 20 sites on the Kennet every month."
The Angling Trust have been involved throughout and have been liaising with both Thames Water and the EA. Their Campaigns Coordinator Martin Salter will be attending the forthcoming meeting organised by the EA to discuss the incident with river keepers and fishery interests.
Mark Owen, Freshwater and Environment Campaigns Manager for the Angling Trust, said: "This is a truly appalling pollution which seems to have been caused by a small amount of lethal pesticide which entered the sewerage system in the Marlborough area. We very much support the work to track down both the source and those responsible for the pollution and our colleagues at Fish Legal are ready to take action on behalf of our member clubs.
"Even if fish stocks remain untouched there is now precious little left for the fish or other wildlife to eat which is why the Angling Trust is calling for measures to try and recolonise the affected stretches with invertebrates as quickly as possible.
"We will support any measures the EA recommend to restore invertebrate communities in a sustainable manner."
Martin Salter added: "The Angling Trust wants to know why on earth a lethal chemical like chlorpyriphos is allowed to be used anywhere near a river or watercourse. Apparently the 15km wipe-out of invertebrates between Marlborough and Hungerford may have been caused by as little as a couple of spoonfuls of the stuff. If this is the case then the sooner we follow the lead of Singapore and America and ban it, the better.
"We shall be asking the Environment Agency to immediately add this chemical to their Watch List of Priority Hazardous Substances to ensure all water bodies are monitored for the presence or absence of this chemical in our rivers."