Campaign group Cymdeithas Eryri have applied for a Judicial Review of Eryri National Park Authority’s decision to grant planning permission for a hydro-electric scheme at Llan Ffestiniog’s Rhaeadr y Cwm waterfall.

Planning permission was given on 15 July despite objections from Cymdeithas Eryri who say, at times, nearly 70 per cent of the water would be diverted away from the waterfall into a plastic pipe, threatening the sensory experience and unique environment of this special place.

The waterfall is located in the Cwm Cynfal Site of Special Scientific Interest and forms part of the wider Migneint–Arenig–Dduallt Special Area of Conservation and Special Protection Area: an internationally important area for blanket bog and upland heath. The site supports rare bryophytes (mosses and liverworts) typical of humid ravines and a range of animals including bats, insects, birds and small mammals typical of ancient Celtic rainforest remnants.

The SSSI also lies wholly within the Eryri National Park and within the Ardudwy Historic Landscape of Outstanding Interest.

Environmental organisations have raised concerns throughout the application process around the potential harmful impacts of reduced waterflows on the sensitive ecology of the local environment, notably the harm that could be caused to rare and declining species of bryophytes. Cymdeithas Eryri are disappointed by the decision to grant planning permission, but also have concerns about aspects of the decision-making.

As a result, Cymdeithas Eryri and their supporters took legal advice and applied to the High Court for a Judicial Review of ENPA’s grant of planning permission.

Their legal team filed a claim for judicial review on 26 August.

A decision on whether they have permission to proceed to a full hearing is likely to be made before the end of 2026 with a final decision unlikely until mid/late 2027.

Cymdeithas Eryri have launched a campaign to help fund the legal costs associated with this Judicial Review – costs that are likely to amount to over £60,000 – and have already secured a pledge of £7,500.

Supporters can donate at www.justgiving.com/campaign/cwm-cynfal.

Cymdeithas Eryri Director Graeme Cotterill said: “Taking this step is unprecedented for Cymdeithas Eryri. In our 60-year history, we have engaged with countless Eryri National Park Authority planning decisions – but this is the first time we’ve legally challenged one. Whilst our close working relationship with the Authority in recent years benefits everybody and we intend it to continue, it is important that we challenge decisions that we and our supporters feel are not made in the Park’s best interest.”

Cymdeithas Eryri is represented by Ricardo Gama, Carol Day, Romany Kisbee-Batho and Lily Hartley-Matthews who said: “The fact Cymdeithas Eyri has taken this unprecedented step demonstrates how seriously it views this decision. This case concerns one of the most iconic waterfalls in Wales and a landscape afforded some of the highest levels of environmental protection available. At its heart, the claim is about ensuring this decision to approve major development in Eryri National Park has been taken lawfully and in accordance with the national and local planning policies intended to protect places of such significance.”