Campaigners knock back Eryri hydroelectric scheme with legal challenge

The challenge brought by Cymdeithas Eryri (Snowdonia Society) saw the Eryri National Park Authority agree to withdraw approval for the scheme, which proposes diverting water away from the iconic Rhaedr y Cwm waterfall.

Campaigners argue the development would negatively impact the waterfall and damage the surrounding environment and wildlife, and say this would outweigh any benefits of the energy generated by the development. 

The park authority accepted one of the grounds of challenge submitted by Cymdeithas Eryri and agreed to quash the plans, which will now be re-reviewed. 

Plans for the hydroelectric scheme were approved through a vote by the park authority’s Planning & Access Committee in June 2026.  

The plans propose the construction of an intake weir and underground pipe from the Afon Cynfal river near Llan Ffestiniog. This would divert, at times, up to 70% of the water at Rhaedr y Cwm waterfall away to be used for electricity production. 

Some 1,590 objections were submitted during the planning consultation process, with Ffestiniog Town Council also sending an objection letter opposing the plans. 

Following Eryri National Park Authority’s vote to approve the plans in June and planning permission being formally granted in July, Cymdeithas Eryri began a judicial review challenge opposing the decision.  

The site of the proposed hydroelectric scheme is partially located in a designated Site of Special Scientific Interest (SSSI), which offers protections to ecologically important land. 

Cymdeithas Eryri argues in its legal challenge that the park authority has misinterpreted or misapplied planning policy for developments that affect SSSIs. They are concerned that the hydroelectric scheme does not do enough to mitigate any environmental damage it might cause to the area, which is afforded special protections due to being a SSSI. 

The group also says diverting water from the waterfall will have a negative visual and acoustic impact, which has been understated in the plans. They have concerns that the proposed level of water abstraction will harm rare bryophyte populations, and that there is a high risk of permanent scarring on the landscape due to the need for a vehicle access track, as well as the potential for erosion damage and sediment pollution. 

The group also argues that the park authority was wrong to accept there was an overriding public need for the hydroelectric development. 

After filing its claim with the High Court in September, Cymdeithas Eryri received confirmation from the park authority that it would consent to the quashing by the court of its decision to approve the hydroelectric development, conceding the first ground of the campaign group’s legal challenge. The ground alleged that the park authority unlawfully failed to advise the Planning Committee that the scheme did not comply with planning policy on development in an SSSI. 

Graeme Cotterill, director of Cymdeithas Eryri, said:

“We are delighted that part of our legal challenge to the decision was accepted as valid without having to hold a full court hearing, and grateful to all involved for this early resolution. However, we recognise that this could be only the first step in an ongoing battle for the future of Cwm Cynfal’s waterfall and wildlife and Eryri’s special qualities as a National Park. We urge decision-makers to continue to consider the other important issues we and other objectors have highlighted, including the lack of the ‘wholly exceptional circumstances’ that Planning Policy Wales is clear should be in place for any work affecting a SSSI. We firmly hope that the first judicial review application in our history will not need to be followed almost immediately by a second.” 

Leigh Day solicitor Lily Hartley-Matthews, who represents Cymdeithas Eryri, said: 

“Our clients are very pleased with this result, with planning approval for the hydroelectric scheme now quashed. Their first ground of challenge argued that the park authority had misinterpreted Welsh planning policy on development affecting an SSSI and failed to advise the Planning Committee that the scheme did not comply with this - an argument which has now been accepted by the park authority. Being compelled to bring a legal challenge is a new position for Cymdeithas Eryri to find itself in, and shows how seriously they feel about protecting the globally renowned landscape at Eryri National Park.”