An ongoing sewage discharge into the River Misbourne for more than 160 hours has “heightened the risk” for local people, a campaigner has said.

Thames Water confirmed that sewage is currently entering the waterway at Gerrards Cross Sewage Treatment Works.

A storm overflow at the site has continuously been discharging into the river since November 1, according to the water company’s live map.

The map tool says: “This means there could be sewage in this section of the watercourse.”

Storm overflows are used to prevent sewers flooding and act as a “safety valve”, diverting some of the rainwater and foul water into watercourses.

The ongoing discharge into the Misbourne presents a safety risk to river users, Paul Jennings, the Chairman of the nearby River Chess Association told the BBC Local Democracy Reporting Service (LDRS).

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He said: “There is a big question as to why there has been this increase in discharges and what has caused that. Yes, we have had wet weather, but we have had we weather in the adjacent valleys.”

The campaigner, who is based in the next valley over, called for greater transparency from Thames Water.

He said: “I would encourage Thames Water to publish detailed plans for Gerrards Cross. It heightens the risk to anybody that using the river downstream from the effluent.

“People get very agitated about the impact on their dogs going in and out of the river, and people working in the river, will it affect them? I’m sure that Thames Water have got it in hand, but it is a problem.”

Thames Water pointed to a planned upgrade of its facilities in Gerrards Cross and the heavy rain last week due to Storm Ciaran after being asked about the ongoing discharge of sewage into the Misbourne.

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A spokesperson told the LDRS: “We regard all discharges as unacceptable and we have published plans to upgrade over 250 of our sewage treatment works and sewers to reduce the number of discharges into watercourses.

“This includes an upgrade to Gerrards Cross Sewage Treatment works, which is planned to be completed by 2026.”

The water company also claimed that it was the first to provide live alerts for all untreated discharges throughout the region, adding that its open data was available for people such as swimming and environmental groups, to use.

Mr Jennings welcomed the upgrades, saying: “On the plus side we are seeing improvements, and they are trying to improve the service.”

The campaigner also said he was worried about the ongoing drilling of two tunnels under the Chiltern Hills for the HS2 high speed railway line.

He said: “I have an underlying concern that is the HS2 works. You have two tunnels going through the aquifer.

“The migration pathways have been changed. You are likely to block the water. But I have got no evidence for this.”