Overview
The blue reservoir near the top of Turlough Hill isn’t natural, and neither is the name. In the heart of the Wicklow Mountains above the Wicklow Gap, this is the site of ESB’s pumped-storage hydroelectric station, a piece of 1960s engineering that quietly helps balance the national grid while staying mostly out of sight inside the mountain. Two things define the hill: the wind-scoured granite ridge under blanket bog, and the geometric artificial reservoir perched near the summit. Below it lies Lough Nahanagan, a natural glacial lake. The difference in height between the two is what makes the power station work.
For walkers, the reward is the height and the view across the neighbouring summits, including Camaderry and Conavalla, with the glacial corrie lake of Lough Nahanagan in the valley below.
The name and history
Before the engineers arrived, the hill was known as Tomaneena, from the Irish Tuaim an Aonaigh, ‘mound of the assembly’. The name Turlough Hill came in the 1960s, when an ESB engineer named O’Riordan called it after his son Turlough during the site surveys; the echo of the Irish turlach, a seasonal limestone lake, is pure coincidence.
When the ESB planned the scheme in the mid-1960s, keeping the view at the Wicklow Gap unspoiled was a stated priority. It brought in landscape architect Sylvia Crowe, who advised planting the upper reservoir’s embankments and shaping the lower works to settle into the rock. To protect the skyline further, the transmission lines were buried for about a mile (1.6 km) out from the site before rising onto pylons down the King’s River valley, a choice that added some £600,000 to the cost but kept the mountain looking much as it always had.
The power station beneath the mountain
Construction began in 1968 and the station entered service in 1974. The principle is simple. Water is pumped uphill from the natural Lough Nahanagan to the artificial reservoir on the ridge when electricity is available to spare. When the grid needs power, the water flows back downhill through pressure tunnels and four reversible units, which together can generate up to 292 MW. The machinery sits in a cavern cut into the granite.
The plant can go from standstill to full output very quickly, which is the whole point of it: catching sudden gaps in supply. The scheme cost IEP £22 million to build, and since 2004 it has also housed the Hydro Control Centre for the ESB’s hydroelectric fleet.
Can you tour it?
Worth knowing before you build a day around it: you can’t just turn up for a visit. The upper reservoir is a working installation behind a fence, and you can’t reach the water. ESB does not run regular public tours of the power station, but occasional tours have been advertised, usually around Heritage Week, and places have booked out fast. Check ESB or the Heritage Week programme for any advertised tours before planning a visit to the station itself, and keep out of operational areas. If there is no tour, the surrounding mountain scenery is the reward on foot.
Walking Turlough Hill
The surrounding uplands are exposed, with rough ground and poor visibility in cloud. If you are planning a hill walk, take a map, check the forecast and choose a route that respects access signs. The upper reaches open into bog with sweeping views once you’re up. The tarmac service road is private ESB property, so follow posted signs at the entrance and keep out of operational areas.
For a marked trail, St Kevin’s Way crosses the Wicklow Gap and continues towards Glendalough. Across the road on the north side of the gap, Tonelagee is a separate mountain and a separate walk.
What to look out for on the trail:
- Glacial features: Lough Nahanagan is a textbook corrie lake, gouged out by ice in the last glaciation and now the scheme’s lower reservoir.
- Alpine flora: For its modest height, the exposed ridge grows plants you’d expect much further north, including dwarf willow, cowberry, crowberry, fir clubmoss and common bilberry, among heather, purple moor-grass and Sphagnum moss.
- Trail conditions: Soft and uneven across the bog. Sturdy boots with ankle support, especially after rain.
- Near the summit: an old quarry edge close to the top has a fence in poor repair, so keep children and dogs close, especially in mist.
Practical information
- Parking: Use the designated Wicklow Gap car park for the mountain scenery and keep the ESB service entrance clear. The tarmac road from the gap to the summit area is the ESB’s private service road behind a barrier, so follow any signage and don’t treat access as a right.
- Best time to visit: Spring through autumn for the steadiest weather and the best of the moorland colour. The summit is exposed to wind and sudden cloud year-round, so check the forecast and pack waterproofs and layers.
- Preparation: Carry a map or GPX file, bring water and food, and follow Leave No Trace. Mobile signal is patchy, so tell someone your route and return time.
- Nearby stops: The Glendalough monastic site and lakes are a short drive down the valley to the east, and the village of Avoca has pubs and cafés for afterwards. St Kevin’s Way, the old pilgrim path to Glendalough, crosses the Wicklow Gap itself.
Don’t plan the trip around a station tour. Come for the scenery and the walk instead, and start early for the quietest parking and the best chance of a clear view.