TWO villages plagued by an "awful pong" for months have had monitors set up around the areas to try and determine the source of the mystery smell.
Locals in Dinas Powys and Sully in Wales have been tormented by the "dreadful" sewage-like stench for weeks and complain it is only getting worse.
In a bid to track down the cause of the stink, 13 odour monitors have now been installed by Welsh Water around its Cogs Moor wastewater treatment works.
The water supplier have so far been left baffled as they cannot establish "the exact cause" but "sincerely apologises".
Dinas Powys councillor Vincent Driscoll said: "It's quite regular now. People in Dinas Powys have been complaining like mad for the last couple of months.
"It's a pungent stinking smell. I can't really describe it — it's horrible.
"There's also been muck-spreading in some farms nearby, so we can't pin it down to the waterworks precisely, but Welsh Water seems to have accepted responsibility."
Dozens of livid locals have shared their frustrations on a local Facebook group - describing the smell as "horrible", "dreadful" and "an awful pong".
One said the relentless odour "can appear all over parts of Dinas at different times/days."
Councillor Driscoll said it seems to be affecting all of Dinas Powys but is "mostly centred on the side closer to the water works".
The Tory councillor said people in Sully have also reported that the stench only seems to be getting worse.
He and fellow Dinas Powys councillor Stephen Griffiths are set to hash out the problem with Welsh Water on Friday.
Water officials said they have deployed teams to "walk the wider area" and speak to residents in a bid to find the source.
They said they have also completed maintenance work on nearby manhole chambers in an effort to stop the puzzling pong.
SNIFF OUT THE STINK
A Welsh Water spokesperson said: "We are carrying out thorough investigations at Cog Moors Wastewater Treatment Works to identify and address the odour issues being reported by residents in Sully.
"As part of this, we’ve installed odour monitors at the site which have identified odour entering the site from our sewer network.
"There are multiple sewer feeds into the site and we have set up odour monitoring on each to identify the source of the odour," they continued.
"In addition, we have also undertaken some maintenance work to nearby manhole chambers to minimise the risk of them releasing any odour from the network.
"At present we do not know the exact cause, but can confirm it is not associated with any releases from our combined storm overflow. While we continue to investigate the source we have put some odour mitigation measures in place which should help reduce the odour level. "
"We sincerely apologise for the inconvenience this is causing residents and appreciate their patience whilst our teams look to find the root cause of the odours," the spokesman said.