A wave of foam heading for Oxford is sweeping down the Thames killing hundreds of fish.

The Environment Agency warned river users to keep away from the foam - which is used by firefighters and came from a chemical spill near Fairford in Gloucestershire - after several people reported minor allergic reactions, including sore throats and itchy eyes.

Last night, it had reached Eynsham Lock. It was expected to hit the city today.

The EA admitted it was unable to clean up the foam and hoped it would disperse and dilute the further downstream it got.

Emma Bateman, the agency officer investigating the spillage, said: "We have received reports that people have suffered from sore throats and itchy eyes if they are near the foam, and if members of the public experience these symptoms they should seek medical advice.

"Fisheries officers are also assessing the impact of the foam on local wildlife and we will continue to do so.

"We won't know exact figures of fish killed until the site has been cleared up properly."

An EA spokesman said it was thought to be hundreds of fish.

She said the foam was not obvious when travelling down the main stretches of river, but bubbled up to heights of up to 6ft when travelling over weirs or through locks.

The EA said it believed it had traced the source of the pollution and its investigation was ongoing. But it refused to reveal how the foam entered the river system due to the possibility of a future prosecution.

The leader of the Green group on Oxford City Council, Craig Simmons, urged the EA to take action.

He said: "The Environment Agency needs to act quickly and firmly to prosecute the people responsible.

"By the sounds of it there is already a severe impact and the EA must act to minimise that damage."

Michael Mann, chairman of Oxford-based Upper Thames Fisheries Consultative, added: "Our general policy is 'the polluter pays'.

"But accidents do happen and it might not have been anyone's fault."

Mr Mann said the group's main concern was the river environment.

He said: "It's the whole ecology not just fish, but all the creatures on which they live."

Boaters near Osney Lock were preparing for the spillage to arrive last night.

Simon Stubbings, 62, of the Osney Island Boat Club, said the fast flowing current would hopefully dilute the foam. He said: "Normally, there's not much of a flow at this time of year and it would have hung around much longer."

The foam was first reported along a 3km stretch of the Dudgrove Brook in Fairford at 7am on Thursday, where it left a trail of dead fish.

A surface water interceptor was blocked off to prevent further discharges, but the foam coursed down the River Colne, which runs into the Thames.

On Thursday night the foam was six feet deep near Lechlade Weir on the Oxfordshire/Gloucestershire border.

If you see the foam send mobile phone pictures to 07834 487010 or email them to yourpix@nqo.com