Llyn Brân

Llyn Brân is located in Denbighshire, just outside Bylchau, on the B5401 between Denbigh and Pentrefoelas. It is a raised natural lake, impounded by a small concrete dam which was built around 1899.

Why we are doing the work

The reservoir was used to supply water to the North Wales Hospital in Denbigh. But since the hospital closed in 1995, the reservoir is no longer part of the water supply network. Dŵr Cymru Welsh Water has now decided to return the reservoir back to a natural lake.

What we are doing?

Over the summer months of 2022 we will:

  • Remove the dam at Llyn Brân. The construction work will involve complete removal of the dam structure, ecological enhancements and shoreline restoration. The work will result in a reduction in surface area of the lake of approximately half (123,500m² to 61,500m²)
  • Demolish ancillary building and associated structure located at the north eastern area of the reservoir. All building waste will be removed for disposal off-site.
  • Exposed sections of pipework will be removed and disposed of off-site. Buried pipework will be sealed and filled by grouting
  • New roadside fencing to be installed along the south side of the A543 at the north end of the reservoir
  • Install a layer of stone to protect the soil surface from erosion. This will be required around the upstream end of the B4501 culvert a short distance downstream of the discontinued reservoir.

What does this mean for the general public?

Our contractors William Hughes Civil Engineering will be working at Llyn Brân for 6 months during the summer and autumn of 2022.

Traffic lights will need to be installed on the B5401 and the A543 during some periods to enable fencing replacement and other construction work.

After the water level at the reservoir is lowered, the site may initially look quite muddy. However, after a growing season, the coir seeded matting will start to grow and re-cover this area.

How we are doing the work

The first phase of the work will involve constructing a temporary access track to the site. The reservoir will then be lowered by approximately 2.4m, taking it back to the natural lake level. This will be done using a system of syphons and pumps to remove the water.

The concrete dam structure will then be dismantled and removed off site. Silt from the reservoir will be placed in specialist silt tubes to drain safely. Remediation works around the shoreline and downstream watercourse will complete the works, with natural coir matting placed around the margins.

Following the reservoir lowering, the site may initially look quite muddy. However, after a growing season, the reservoir margins will begin to re-naturalise and will be monitored by specialist environmental consultants over a number of years.


Protection of the environment has always been at the forefront of this project.

We have worked closely with Natural Resources Wales (NRW) and specialist environmental consultants Ricardo throughout this scheme. Detailed ecological surveys, assessments and mitigations have been made to ensure the work does not cause a negative impact to the environment.

Dam removal is widely recognised as being beneficial to the environment and NRW is supportive of the work we are doing. By removing the dam structure at Llyn Brân, we will see an improvement in the local biodiversity of the area. In fact. the work at Llyn Brân will result in the site becoming a Special Area of Conservation (SAC).

We are also turning Llyn Anafon reservoir near Llanfairfechan back to a natural lake. As a compensatory measure, some rare plants from Anafon will be transferred to Llyn Brân to increase the resilience of the species.

Timeline of work

The work is due to start during May 2022 and will last until October 2022. Ongoing Ecological monitoring of the lake will continue until winter 2024.

After the work

Immediately following the lowering of the water, the edges around the lake may look muddy as silt becomes exposed. These areas will be covered with natural seeded matting, which will start to grow throughout spring / summer 2023. As the mats grow and establish, the site will look begin to re-naturalise. The matting will not cover the whole area of the exposed edges and will seed naturally over time. Pre-vegetated matting will be installed in some areas which will form part of the habitat restoration for the water vole population at Brân.