A campaigner for keeping Kings Pond believes another pollution incident has shown the difficulty of achieving the River Wey chalk stream dream.

An Alton Town Council internal email confirmed that “discoloured and smelly water” was flowing into the pond from an inlet on October 11.

In a statement late on October 14, Thames Water said: “Thames Water has been investigating a foul water pollution incident at Kings Pond since October 11. It deployed mitigation measures to prevent any further pollution and is working to fix this as quickly as possible.

“Thames Water is also carrying out regular water quality assessments and managing the situation to ensure no pollutants enter the pond. If you have reports of further incidents, please call Thames Water on 0800 316 9800.”

Alton Town Council is considering two options for the pond’s future - dredging it, or separating it from the River Wey in a bid to turn the river into a chalk stream wildlife habitat.

But Anthony Furnival, of the Kings Pond Preservation Society, thinks this is impossible without dealing with pollutants flowing into the pond from upstream.

Mr Furnival, who photographed dirty water entering the pond from a drain in April, said: “Such pollution events highlight the inherent flaw in the offline model the council has been investigating.

“The sheer volume of run off and discharge into the Wey between its source and Kings Pond are a significant barrier to achieving the ecological conditions of a genuine chalk stream habitat, notably the characteristically pure water of such environs. While drains and other sources of ingress can be diverted, the bill could run into millions.

“The retention of the pond alongside mitigation to improve water quality and biodiversity, on the other hand, will not only protect the wildlife we have but offer far greater value to the council tax payer.”

Cllr Ginny Boxall, who represents Alton Whitedown on East Hampshire District Council, said: "Any incident of pollution in the River Wey is very worrying.

"I know that Alton Town Council is carefully exploring all the options for the future of the pond and river. The northern River Wey is a chalk stream and over the years a great deal of effort has gone into trying to improve it for aquatic biodiversity.

"I believe we should strengthen protections for all East Hampshire chalk streams and rivers, and I am bringing forward a motion on this in November at East Hampshire District Council's full council meeting, with help from the Hampshire and Isle of Wight Wildlife Trust, which will give a briefing to all councillors in early November on why we should adopt the motion."

A spokesperson for Alton Town Council added: "It was reassuring that Thames Water responded quickly to their leak. The implications of such an incident, even if rare, will need to be considered for whatever option is proposed for Kings Pond."