Llyn Celyn improvement work


Llyn Celyn reservoir is our largest reservoir in north Wales and plays an essential role in helping to provide clean, fresh drinking water.

It also plays an essential role in regulating the level of the River Dee to protect its aquatic life and to facilitate water-based activities downstream at the National White Water Centre for Wales.

The reservoir also forms a major part of Wales’ history after the residents of the village of Capel Celyn had to move out to make way for the reservoir. A memorial chapel, which has recently been restored by Dŵr Cymru Welsh Water, sits on the banks of the reservoir to commemorate this.

What is happening?

We take our responsibility for safely maintaining and operating dams seriously at Welsh Water. To do this, we have all of them regularly inspected by independent dam engineers. Llyn Celyn was inspected in this way in 2019 using the latest and current guidance for reservoirs and dams in the UK.

In 2020, the inspection report was completed confirming that Llyn Celyn reservoir is in a good state but as expected, it made some recommendations to meet the latest guidance.

The recommendations in the final report are statutory and are enforced by Natural Resources Wales. Welsh Water must respond to them within a defined timescale. Please be assured that this does not mean there is any immediate safety concerns with the dam.

One of the recommendations was to introduce measures to deal with any overspill at the reservoir that did not rely on manual intervention. At present, control is supported by a series of valves and pipework situated in the tower and the dam structure and is managed by staff on site. The dam already has one spillway, although the water at Llyn Celyn hasn’t risen to this level since the 1970’s.

Welsh Water has considered numerous options to deal with an overspill for extreme water levels and will, in the coming months, submit a planning application to Snowdonia National Park Authority. The proposal is to build a new additional spillway to deal with exceptionally high water levels that could potentially happen in the future.

Our plans will see an upgrade to the reservoir and will ensure resilience for future generations.

Welsh Water’s contractors, Mott MacDonald Bentley (MMB), will oversee this project and please be assured that they will ensure all of the work is done with the least impact possible on local habitats and wildlife.

Keeping everyone informed

As a company, we are committed to keeping customers and stakeholders informed of any work we undertake and will be doing the same here at Llyn Celyn. We are liaising closely with our regulator Natural Resources Wales on the work and our investigations. We are also liaising with Snowdonia National Park Authority.

Further details about the proposed plans are available online between October 28th 2021 and November 15th 2021 with live sessions scheduled to ask questions.

You can chat to our project team during our live Q&A sessions on:

  • Wednesday 10th November 2021 – Drop-by session Frongoch Camp lay-by LL23 7NT 1300-1600
  • You can also visit the online event via https://llyncelyn.com/ at any time during these two weeks and you’ll get the chance to find out more about the project and send us a message with your questions.