Llyn Celyn is a large reservoir constructed in 1961 in the valley of the River Tryweryn in North Wales.
Construction and opposition
Construction of the reservoir involved flooding the village of Capel Celyn and adjacent farmland, which caused considerable outrage in Wales and is still remembered with anger. In all some 16 farms, totalling 770 acres, were affected by the scheme]. Much of the anger was occasioned because the village was a strong-hold of Welsh culture and the Welsh language, whilst the reservoir was being built to supply Liverpool with water with no benefit to Wales. Liverpool City Council were able to get the legislation enabling the drowning of Capel Celyn passed at Westminster even though 35 out of 36 Welsh Members of Parliament voted against it, with the 36th not voting. This led to an upsurge in support for Plaid Cymru in Wales. Roadsigns and even the road surface were daubed with the slogan 'Cofiwch Dryweryn!'- Remember Tryweryn! In October 2005, Liverpool City Council passed a public apology for the incident.
Operation of reservoir
The reservoir was constructed in order to support the water abstractions from the River Dee as part of the River Dee regulation system, including the abstraction by North West Water at Huntington water treatment works, Chester, from where water is supplied to Liverpool and the Wirral. The reservoir is contained behind a rock gravity dam and, at its upper end, it is squeezed between Arenig Fawr and Arenig Fach, two of the mountains of south Snowdonia.
Water is released from the reservoir into the River Tryweryn which then flows into the River Dee. Most releases pass through a small hydro-electricity plant to supply green electricity to the National grid. The released water first flows into a stilling basin and then down the narrow and rocky valley of the River Tryweryn. This section of river provides facilities for international level white-water canoeing, and rafting at the Canolfan Tryweryn National White-water Centre. Some water in the reservoir is held in reserve to make special release down the river for specific white-water events. Because the reservoir's principal purpose is to support low river flows in the main River Dee, the best conditions for white-water occur during long dry spells in summer when maximum releases are made. Usually the dam will release between 9 and 11 cumecs (m�/s) although releases as low as 7m�/s and as high as 16m�/s have been known. During wet weather the releases are throttled back to a minimal maintenance flow.
Diversions/closures of transport links
The building of the reservoir also contributed to the final closure of the GWR branch line from Bala to Blaenau Ffestiniog. Passenger trains had ceased in 1960, and the last freight train ran in 1961. The line was subsequently flooded by the lake, and the base of the dam also crosses it. Liverpool Council had in fact planned a railway diversion, but this was never built. A new main road, the A4212 was built across the pass from Bala to Trawsfynydd around the north side of the lake.