Flooded Eryri sewage plant raises pollution fears in iconic lake
Sewage plant flooding has raised pollution fears in one of the best known lakes in Wales. Llanberis Wastewater Treatment Works were overwhelmed during Storm Bert leaving large parts of the site under water.
A resident filmed water gushing up into the site through what was assumed to be a manhole cover. The Eryri plant discharges into a river that feeds into Llyn Padarn, a two-mile lake renowned for its watersports.
On Saturday evening, November 23, a sewage alert was issued for the lake by Surfers Against Sewage, and this remains in place. Dŵr Cymru data shows at a storm overflow in Afon y Bala, into which treated water is discharged, has operated for 27.68 hours over the past two days. Get all the latest Gwynedd news by signing up to our newsletter.
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Dŵr Cymru Welsh Water (DCWW) investigated the weekend flooding and ruled out a pollution risk to the lake. The company said the plant, which lies beneath Dolbadarn Castle, was “operating as it should”.
A concerned resident came across the sewage plant flooding on Sunday morning. He said: “Most of the surplus water seemed to be bubbling up from underground. It’s difficult to know where this might have come from - perhaps discharge pipes were backing up due to high river levels.
“The water seemed to be flowing into the round treatment beds they have on the site, which was worrying. A pump was working furiously, trying to clear the water from the compound. Similar flooding occurred here last winter, though not as bad. On the occasion, a tanker was brought in to remove what I assumed to be contaminated water. But given the amount of water there this time, there’s no way they can clear it all using tankers.”
The incident has alarmed people who use Llyn Padarn for swimming and paddleboarding. “I thought Llyn Padarn was an SSSI?” said one man online. “Disgusting and beyond a joke now.” Join the North Wales Live WhatsApp community group where you can get the latest stories delivered straight to your phone
Llanberis sewage treatment works discharges secondary treated final effluent into the Afon y Bala. Chemical dosing and sand filtration removes excess nutrients prior to discharge. The small Nant Peris sewage plant upstream discharges secondary-treated effluent into the River Seiont, which also drains into Afon y Bala via a tunnel.
As well as the Llanberis plant, storm overflows operate intermittently into Llyn Padarn from two pumping stations in the village. In recent years, improvements have been made to both Llanberis and Nant Peris sewage works. In the five years to 2023, Llyn Padarn’s water quality has been rated “excellent” and the lake is on course to receive the same rating in 2024.
Over the past four years, sampling and visual inspections by Natural Resources Wales (NRW) staff have revealed no oil or sewage debris in the lake. Trace amounts of animal faeces were detected on a minority of occasions. Biggest issue is the “trace amounts of litter” seen on more than half of all NRW visits.
Dŵr Cymru said flood investigations were carried out at the Llanberis plant following the weekend flooding. A spokesperson said: “The works was operating as it should.
“The flooding was the result of treated wastewater being prevented from going into the watercourse by the high water levels. This floodwater was pumped back into the start of the works so it could be treated again. In line with our policy of being open and transparent we have informed NRW.”
Huw Jones, NRW's environment team leader, said investigations were continuing at the Llanberis sewage plant. He stressed storm overflows occurred only during heavy rain to relieve pressure on sewage systems. Otherwise, raw sewage could be forced back into homes and gardens. Discharges of untreated sewage are "greatly diluted" by rain and so risks to the environment are "drastically reduced", he said.
Mr Jones added: “We have been in close contact with DCWW following the very high rainfall and serious flooding experienced in Wales over the weekend. The scale of rainfall means that sewage systems will have been overwhelmed in many places and storm overflow discharges will have taken place.
“We are looking into whether wider issues beyond rainfall caused the sewage works in Llanberis to become inundated.”
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