THE Environment Agency is investigating ‘serious’ pesticide pollution in the River Kennet, which supplies some drinking water to south Swindon, as campaigners fear an ecological disaster.

Conservation workers from Action for the River Kennet have been monitoring it over the past weeks after the water became cloudy.

On Monday, ARK’s riverfly monitoring team identified a devastating pollution incident on the River Kennet. All the invertebrates for around 15km of river had been killed by a pesticide that entered the river from, or close to, the sewage treatment works at Marlborough.

A spokesman for Thames Water said the drinking water for Swindon was not thought to be affected.

ARK director Charlotte Hitchmough said: “The water had been a funny colour for a long time, caused by an algal bloom, and we were watching it carefully as it was a cause for concern.

“Then suddenly on Sunday, the water went clear. At first we were very pleased but then we tested the water and found that all the invertebrates – the bugs that the fish and birds eat – had disappeared.

“So, obviously some kind of insecticide has entered the water. We don’t know exactly where it has come from but the river downstream of Elcot Lane for 15 kilometres is without any invertebrates while upstream is healthy.

“You can’t see any difference in the river at the moment but you will in the future. There will be a big impact. Those little bugs at the bottom of the river are so important. It would be like killing all the grass in a field so the cows had nothing to eat.”

Ms Hitchmough added: “At the moment we don’t know where this pollution has come from. Because it seems to have started at Elcot Lane the sewage treatment works are in the frame but there are a number of sources it could have come from.”

The Environment Agency has been contacted and they carried out their own investigation on Tuesday.

A spokesman said: “We were made aware of a pollution incident on the River Kennet at Marlborough over the weekend, which killed aquatic invertebrates.

“The pollution has now stopped and we are investigating the cause and the source of the pollutant. Environment officers have taken soil samples and ecology samples to help us identify the source.”

There is no evidence the pollution has any connection with the convoy of tankers taking sewage round the clock from the pumping station at Bay Bridges on the A346, where a pipe had collapsed, to the treatment plant at Elcot Lane.

The work to repair the pipe at the pumping station finished on Tuesday.

A Thames Water spokesman said yesterday: “Tankering of sewage from the Bay Bridge pumping station to the nearby sewage works has ended.

“We’re sorry for any inconvenience this caused and would like to thank customers for their patience as we carried out this tricky repair.”

The Environment Agency is appealing for information on the source of the contamination and anyone with any information should contact 0800 807060 immediately.