Maentwrog site

Maentwrog is a hydroelectric power station located close to the Trawsfynydd site in Gwynedd, that has been at the forefront of renewable energy for almost a century.

Its construction in the 1920s was a remarkable engineering achievement. The project created what was then the second largest reservoir in Wales, supported by four concrete dams holding back 33 million cubic metres of water.  The original main arch dam was the largest of its kind at the time, stretching 3,000 metres. In 1991, it was replaced by the distinctive S‑shaped arch dam seen today.

The 30‑megawatt station sits on the banks of the Dwyryd estuary and has been generating green energy since 1928. Rainfall from the surrounding area is collected through a network of rivers, leats and streams, feeding into Llyn Trawsfynydd, around three miles away.

From there, water is carried by pipeline to drive two turbines, producing enough electricity each year to power around 12,000 local homes.

Maentwrog is unlike any other NRS site. Alongside operating the power station, the small on‑site team also manages the natural resources across its 35‑square‑mile rainfall catchment area.

The station closes annually for essential maintenance. During the 2024 maintenance outage, the Unit 1 turbine generator underwent a major ten‑year overhaul. The high‑pressure pipeline footbridge was replaced in 2021, ensuring the continued safe and reliable operation of the site.

Business updates relating to Maentwrog hydro-electric power station are provided at Trawsfynydd SSG meetings.