Eryri National Park Authority in Wales has agreed to withdraw planning approval for a proposed hydropower scheme near Llan Ffestiniog following a legal challenge by Cymdeithas Eryri (Snowdonia Society).
The authority accepted one ground of the group’s judicial review claim concerning planning policy for development affecting a Site of Special Scientific Interest (SSSI). The application will now be reconsidered.
The proposed scheme would involve constructing an intake weir on the Afon Cynfal and an underground pipeline to divert water for electricity generation. At certain times, the scheme could divert up to 70% of the water away from Rhaedr y Cwm waterfall.
The authority’s Planning & Access Committee voted to approve the development in June 2026, with planning permission formally granted in July. Around 1,590 objections were submitted during consultation, while Ffestiniog Town Council also opposed the plans.
Cymdeithas Eryri filed its judicial review claim with the High Court in September. The authority subsequently confirmed that it would consent to the court quashing its approval decision. It accepted the group’s argument that it had unlawfully failed to advise the planning committee that the scheme did not comply with planning policy on development affecting an SSSI.
Part of the proposed development lies within an SSSI. Cymdeithas Eryri argues that the scheme does not adequately mitigate potential environmental damage and that its effects on the waterfall’s appearance and sound have been understated.
The group also raised concerns about potential harm to rare bryophyte populations, permanent landscape scarring from a vehicle access track, erosion and sediment pollution. It disputes the authority’s assessment that there was an overriding public need for the development.
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.”
He added: “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: “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.”
