Liverpool and Wirral. The reservoir is contained behind a rock gravity dam and, at its upper end, it is bounded between Arenig Fawr and Arenig Fach, two of the mountains of south Snowdonia. Water is released from the reservoir into the River Tryweryn which flows into the River Dee. Most of the water passes through a small hydro-electric 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 the 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 be released down the river for specific whitewater events. Because the reservoir's principal purpose is to support low river flows in the main River Dee, the best conditions for such events occur during long dry spells in summer when maximum releases are made. Usually the dam will release between 9 and 11 m³/s, although releases as low as 2 m³/s and as high as 16 m³/s have been known. During wet weather the releases are usually throttled back to a minimal maintenance flow unless a planned release for recreational activities has been agreed. Its four turbines are owned and run by Dŵr Cymru and generate 4.38 MW Diversions and closures of transport links The building of the reservoir also contributed to the final closure of the Great Western Railway (GWR) branch line from Bala to Blaenau Ffestiniog. Passenger trains had ceased running 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 as the British Transport Commission had decided to close the line. As a result of this, Liverpool Council decided to contribute towards the cost of the new main road (the A4212, which was built across the pass from Bala to Trawsfynydd around the north side of the lake), and also towards the cost of a line linking the two stations in Blaenau Ffestiniog. See also Cofiwch Dryweryn References External links Abandoned communities ..... Llyn Celyn Drowning of Tryweryn, 1965 Clip from 1969 BBC factual programme The Sixties with archive footage. Llandderfel Llanycil River Dee, Wales Celyn Celyn River