Illegal rubbish heap, located beside the A34 and the River Cherwell, stretches 500ft and contains plastic, foam and wood

Fly-tippers have dumped a river of waste in rural Oxfordshire.

The illegal rubbish heap - described as "an environmental catastrophe unfolding in plain sight" - is around 20ft high, stretches 500ft long, and contains plastic, foam and wood.

It is believed to have been dumped in one go next to the A34 and River Cherwell, near the village of Kidlington, and was discovered last month by anglers. Some of the rubbish is said to be just five metres away from the river.

Friends of the Thames, an environmental charity, said the dump was created by an organised crime group. Laura Reineke, the charity's chief executive, told the BBC: "This is an environmental catastrophe unfolding in plain sight.

"Every day that passes increases the risk of toxic run-off entering the river system, poisoning wildlife and threatening the health of the entire catchment. The Environment Agency must act now, not in months or years, which is their usual reaction time."

The Environment Agency has confirmed an investigation has been launched and has encouraged anyone with any information to get in touch as soon as possible. A spokesman said: "The Environment Agency is aware and investigating. If anyone has any information then please call independent charity Crimestoppers anonymously on 0800 555 111."

Calum Miller, the Liberal Democrat MP for Bicester and Woodstock, raised the issue in Parliament. Addressing MPs on Thursday, he said: "Criminals have dumped a mountain of illegal plastic waste... weighing hundreds of tonnes, in my constituency on a floodplain adjacent to the River Cherwell.

"River levels are rising and heatmaps show that the waste is also heating up, raising the risk of fire. The Environment Agency said it has limited resources for enforcement, that the estimated cost of removal is greater than the entire annual budget of the local district council."