Volunteers say recent bad weather has triggered ‘the usual overflow’ of sewer systems – with an ongoing, 170-hour-and-counting discharge in Gerrards Cross something that ‘just shouldn’t be happening’.

The River Misbourne through Amersham and the Chalfonts has seen disproportionate levels of flooding over the last 12 months, with high water levels and sewage leaks turning villages into “open sewers” last winter.

It reached such a breaking point that the Environment Agency declared a ‘category one’ pollution event – denoting a serious, extensive or persistent impact on the environment – and Chalfont St Giles was forced to withdraw from the annual Best Kept Village competition.

While the pressure has been off and normalcy gradually resumed over the drier summer months, record rainfall last week hit many of the riverbank’s weak spots hard and, though it was short lived, has caused local concern over what the winter and autumn has in store.

Bob Older, founder of the Misbourne River Action group, a non-profit aimed at protecting the chalk waterway, said that while he had been in meetings with Thames Water, the Environment Agency and Buckinghamshire Council in recent weeks, “no one assumes much is going to change in the next year or so” – a precarious position from which to face the UK’s colder and wetter months.

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He also described a still-discharging overflow at the Gerrards Cross sewage treatment plant, which began more than 177 hours ago on Monday, September 23, as something that “just shouldn’t be happening” and will doubtful be fixed by Thames Water’s attempts to "develop short-term solutions through maintenance work” along the Misbourne.

Thames Water has repeatedly said that storm overflows are more likely to discharge excess waste and rainwater following heavy downpours – with the system preventing the build-up from overwhelming the pipe network and backing up into people’s homes and streets.

A criticism frequently levied at the water company, however, is that its infrastructure to handle such discharges is just not up to scratch – and upgrades planned for a number of sewage treatment works including at Gerrards Cross are not likely to be finished for at least three years, leaving those impacted by the flooding on a day-to-day basis in limbo.

Bob said: “The situation in Gerrards Cross is polluting the water going down to Denham in the lower part of the Misbourne – it’s not as bad as what we saw in Chalfont St Peter last winter, but it is still happening. The usual overflows are impacted every time.

“The truth is that the works just aren’t big enough to cope. I think the guards in place to prevent this kind of thing have reached a critical breaking point.”

Thames Water was contacted for comment.