Llyn Bran

Llyn Bran 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. The reservoir was used to supply water to the North Wales Hospital in Denbigh and was owned by The Welsh Hospitals Board.

In 1988 the ownership of the reservoir passed to Welsh Water.  In 1995 the North Wales hospital was closed the reservoir was no longer used for water supply and has not been used since. 

What we are doing on site

We will be carrying out work to remove the dam at Llyn Bran.  This will mean that the reservoir will return back its former state as a natural lake instead of being artificially raised. 

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).

Why we are doing the work

Llyn Bran has not been used for water supply since 1995 and will not be used in future.  It has therefore been decided to remove the dam and return the reservoir back to a natural lake.  This will result in a number of ecological benefits, as well as removing the ongoing costs associated with maintaining a dam structure.  

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 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 seeded 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 as the coir seeded matting grows and establishes.


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 Bran, we will see an improvement in the local biodiversity of the area.  In fact. the work at Llyn Bran will result in the site becoming a Special Area of Conservation (SAC).

Timeline of work

The reservoir will be lowered during March 2022. The work will last until May 2022, with ongoing ecological monitoring of the lake continuing until summer 2023. 

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 2021. As the mats grow and establish, the site will look begin to re-naturalise.