Sewage has been streaming through back gardens in Venton Road, Falmouth, following attempts by South West Water to prevent waste water flooding a path in Tregoniggie Woods.

Following recent in the woods, South West Water installed a limiter to divert waste water from one sewage pipe to a higher pipe, but the measure appears to have caused sewage to overflow the upper pipe at certain times, flooding into a stream which runs through two gardens before returning to the main watercourse and entering Swanpool nature reserve.

David Evans, the deputy chairman of Friends of Tregoniggie Woodland and the owner of one of the affected houses, said that just one day after South West Water had announced its temporary fix to the pipe, there was a "torrent" of water running through the bottom of his garden, and "there was definitely sewage in there."

"Since they've diverted," he said, "it's started rushing through like a torrent. It has been clear, but where the sewage has been it's killed everything off.

"We have got the sediment of the sewage that's settled in the bottom of the stream, when they tested the water it was 25 per cent sewage."

He added: "We did have frogs down in the silt of the stream for the winter, but whether they will survive I don't know."

Mr Evans said the water could change "in an hour" from clear to sewage, and raised concerns that after it had run through his property and his next door neighbour it would return to the main stream running through Tregoniggie and from there could contaminate the nature reserve downstream.

Euan McPhee, the chairman of the friends group, said while he was delighted that South West Water were trying to fix the problem in the woodland, and while the company had admitted it was an interim solution, "obviously these people on Venton Road are not satisfied."

He also questioned, if sewers are currently unable to cope with the volume of water, how much worse it would be if planned housing developments were added to the system. He said he believed the only solution would be a complete upgrade of the system, and asked whether this would be funded by South West Water or whether Cornwall Council would be able to demand that developers contribute to the cost.

South West Water said the problem had been caused by items such as wipes completely blocking the lower sewage pipe, restricted as part of the temporary fix, which forced all the waste water into the higher sewer.

A spokesperson said: "This other sewer is now intermittently surcharging, and waste water appears to be finding its way into a buried culvert, which appears above ground in the vicinity of Venton Road and runs through a resident’s garden. The volume of rain water entering the network may be forcing a joint open or it is possible there is a split in the pipe.

"We intend to investigate further using CCTV cameras to survey the pipes, but this has not been possible yet due to the ongoing wet weather. We are of course keeping those affected updated."