A landmark engineering project in Gwynedd has earned national recognition, winning Water Project of the Year at the British Construction & Infrastructure Awards 2025.

Dŵr Cymru Welsh Water’s project to install a new spillway at Llyn Celyn reservoir has received the honour.

Delivered in partnership with Mott MacDonald Bentley (MMB), the project represents a major step forward in dam safety and climate resilience. The innovative scheme provides a significant safety upgrade to the reservoir—ensuring resilience, sustainability, and protection for communities and the environment for generations to come.

The project’s centrepiece is a new auxiliary spillway featuring 4.5-metre-high tipping gates—the first of their kind in the UK at this scale. Designed to operate only during exceptionally rare flood events, the system enhances the dam’s ability to manage probable maximum flood scenarios, with a design life of over 100 years.

Dŵr Cymru Project Manager Karen Morris said: “Winning this award is a testament to the dedication and expertise of everyone involved in the Llyn Celyn project.

“Our commitment to safety, innovation, and environmental conservation has delivered a resilient solution that will protect communities and the environment for decades to come.

“We are especially proud of the collaborative working shown by our teams and partners, and grateful for the support of local stakeholders throughout the process.

“The project has showcased partnership working between ourselves in Welsh Water and Natural Resources Wales along with our contractors and numerous stakeholders. This has been one of our largest projects that we’ve undertaken in Welsh Water over the past few years combines technical excellence with real social and environmental value.”

Mott MacDonald Bentley Design Manager Michael McAree said: “We are delighted to have worked alongside Welsh Water on this pioneering scheme. The success of the Llyn Celyn project reflects the strength of our partnership, the ingenuity of our engineering teams, and our shared commitment to delivering safe, sustainable solutions.

“The project’s innovative spillway design and digital delivery approach have set new standards for the sector.”

Keith Ivens, Operations Manager for Flood and Water Management at Natural Resources Wales, said:

“We’re delighted the Llyn Celyn reservoir safety works have been recognised as Water Project of the Year at the British Construction & Infrastructure Awards 2025. This milestone marks the successful completion of a decade-long programme, delivering a new spillway to safeguard the dam’s integrity and ensure it can safely operate in the most extreme situations.

“Llyn Celyn plays a vital role as the primary source for the River Dee Regulation Scheme, which supplies water to over 2.5 million people and provides essential flood alleviation for downstream communities. This achievement reflects outstanding collaboration between Dŵr Cymru and NRW teams, overcoming challenges from extreme weather to the pandemic. We’re proud to have contributed to a project that strengthens resilience and protects people and the environment for generations to come.”

The spillway’s design incorporates a culverted structure for two-thirds of its length, minimising visual impact and preserving the natural landscape of Eryri National Park.

Work started on site in 2023 and will be completed by the end of 2025.