Tucked away in the remote green hills of mid-Wales lies one of Britain’s greatest feats of post-war engineering, yet most people outside of Wales have never even heard of it.

The Claerwen Dam, near Elan Valley in Powys, is the largest dam in the UK, holding back an astonishing 48 billion litres of water, enough to supply millions of homes and businesses for months on end. Built in the 1950s, the dam was part of a massive national effort to future-proof the UK’s water supply in the wake of wartime shortages. 

And unlike today’s high-tech construction projects, this colossus was built with sheer manpower.

Engineers and labourers, many of them veterans, blasted their way through mountains with dynamite, shifting thousands of tonnes of rock with only the most basic tools.

Working in gruelling conditions, they endured bitter winters, remote living quarters, and months without seeing their families.

The cost of the project at the time was £6 million, a staggering sum for the era, but the human cost was even greater. The vast valley behind the dam, now a serene reservoir, was once home to farms, homes, and even a small village, all of which were lost beneath the rising waters.

The site was chosen for its natural basin and ability to collect rainfall in high volumes, but for those who once called the valley home, the project brought heartbreak.

Today, the Claerwen Dam stands 56 metres high and stretches 355 metres across, blending beautifully with its surroundings thanks to its traditional stonework, a deliberate design choice to match the earlier Victorian dams nearby.

Despite its scale and importance, the Claerwen Dam remains largely unknown to the general public, hidden in plain sight among the rolling Welsh hills.

Yet without it, much of England and Wales would have faced severe droughts in recent decades.