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There are a large number of reservoirs in Wales reflecting the need for the supply of water for both industry and for consumption, both within the country itself and in neighbouring
England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...
. A number also provide hydroelectricity and many old reservoirs also provided motive power for industries, especially for the processing of minerals such as metal ores and slate. Wales has a relatively high rainfall and significant areas of mountainous topography which are sparsely populated which ensures that water is a plentiful
natural resource Natural resources are resources that are drawn from nature and used with few modifications. This includes the sources of valued characteristics such as commercial and industrial use, aesthetic value, scientific interest and cultural value. O ...
. Much of the south and east of England has significantly lower rainfall and a high population density which puts significant strain on the water supply infrastructure there. Collecting water in deep valleys with high river flows is far more efficient that trying to collect sparse rainfall in a generally flat landscape. Because of this engineers have viewed Wales as a potential supply of water. The rapidly growing populations of the industrial centres of Britain in the
industrial revolution The Industrial Revolution was the transition to new manufacturing processes in Great Britain, continental Europe, and the United States, that occurred during the period from around 1760 to about 1820–1840. This transition included going f ...
made the need for high volume supplies of clean water even more important and Wales was seen as the ideal source. Such engineering and economic views paid scant regard to the social, cultural and linguistic impacts that the constructions of large reservoirs in Wales would create. Some reservoirs have been formed by the raising of dams on water courses, others are natural water bodies, the levels of which have been raised to various degrees both for direct supply of water or else for regulation of supply with water being extracted from the river some way downstream. Many reservoirs which were constructed for one purpose e.g. industry, may now serve different or additional purposes e.g amenity or, as in many cases, have been abandoned entirely. Reservoirs range in size with many under 1 acre in area serving local needs, up to
Llyn Trawsfynydd Llyn Trawsfynydd is a large man-made reservoir situated near the village of Trawsfynydd in Gwynedd, North Wales. With a total surface area of the reservoir is slightly more extensive than Wales's largest natural lake, Llyn Tegid at . History ...
which extends to .
Bala Lake Bala Lake ( cy, Llyn Tegid ) is a large freshwater glacial lake in Gwynedd, Wales. The River Dee, which has its source on the slopes of Dduallt in the mountains of Snowdonia, feeds the long by wide lake. It was the largest natural body o ...
(
Welsh Welsh may refer to: Related to Wales * Welsh, referring or related to Wales * Welsh language, a Brittonic Celtic language spoken in Wales * Welsh people People * Welsh (surname) * Sometimes used as a synonym for the ancient Britons (Celtic peop ...
''Llyn Tegid'') is a natural lake which at , slightly exceeds Llyn Trawsfynydd in size, but whose height has been slightly raised.


Water supply to England

Most Welsh lakes supply the nation itself with water, however, there are lakes and reservoirs which supply England. In the early
1960s File:1960s montage.png, Clockwise from top left: U.S. soldiers during the Vietnam War; the Beatles led the British Invasion of the U.S. music market; a half-a-million people participate in the 1969 Woodstock Festival; Neil Armstrong and Buzz ...
, 70 people were forced to leave their homes in
Capel Celyn Capel Celyn was a rural community to the northwest of Bala in Gwynedd, Wales, in the Afon Tryweryn valley. The village and other parts of the valley were flooded in 1965 to create a reservoir, Llyn Celyn, in order to supply Liverpool and Wirral ...
before the whole valley was drowned, and the
Llyn Celyn Llyn Celyn () is a reservoir constructed between 1960 and 1965 in the valley of the River Tryweryn in Gwynedd, Wales. It measures roughly long by wide, and has a maximum depth of . It has the capacity to hold of water. It was originally ...
reservoir built in order to supply water to
Liverpool Liverpool is a city and metropolitan borough in Merseyside, England. With a population of in 2019, it is the 10th largest English district by population and its metropolitan area is the fifth largest in the United Kingdom, with a popul ...
,
England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...
, 60 miles (95 km) away. Birmingham Corporation had one hundred occupants moved out of their homes in the
Elan Valley The Elan Valley ( cy, Cwm Elan) is a river valley situated to the west of Rhayader, in Powys, Wales, sometimes known as the "Welsh Lake District". It covers of lake and countryside. The valley contains the Elan Valley Reservoirs and Elan Villag ...
,
Powys Powys (; ) is a Local government in Wales#Principal areas, county and Preserved counties of Wales, preserved county in Wales. It is named after the Kingdom of Powys which was a Welsh succession of states, successor state, petty kingdom and princi ...
, in order to build the reservoirs. Wales has its own water company, Dŵr Cymru, but two water companies operate across the border namely
Severn Trent Water Severn Trent plc is a water company based in Coventry, England. It supplies 4.6 million households and business across the Midlands and Wales. It is traded on the London Stock Exchange and a constituent of the FTSE 100 Index. Severn Trent, the ...
and
United Utilities United Utilities Group plc (UU), the United Kingdom's largest listed water company, was founded in 1995 as a result of the merger of North West Water and NORWEB. The group manages the regulated water and waste water network in North West Englan ...
.


Reservoirs in Snowdonia


Local water supply

Within Snowdonia, numerous existing natural lakes were co-opted to provide local water supplies during the late 19th and early 20th centuries. Within the
Carneddau The (lit. 'the cairns'; is a Welsh plural form, and is sometimes anglicised to ''Carnedds'') are a group of mountains in Snowdonia, Wales. They include the largest contiguous areas of high ground (over or high) in Wales and England (although l ...
,
Llyn Dulyn Llyn Dulyn ( cy, black lake) is a lake on the edge of the Carneddau range of mountains in Snowdonia, North Wales. The lake is in extent and 189 feet (58 metres) deep. Less than a kilometre to its south lies the smaller Llyn Melynllyn. Cliffs ris ...
and
Llyn Melynllyn Llyn Melynllyn (Welsh for ''yellow lake'') is a lake within the Carneddau range of mountains in Snowdonia, North Wales. It lies at a height of just over , and has an area of some . Cliffs rise steeply from its western edge, up to the summit of ...
were dammed in 1881 and 1887 respectively, to provide water to
Llandudno Llandudno (, ) is a seaside resort, town and community in Conwy County Borough, Wales, located on the Creuddyn peninsula, which protrudes into the Irish Sea. In the 2011 UK census, the community – which includes Gogarth, Penrhyn Bay, Craigsi ...
whilst Llyn Anafon was dammed in 1930 to do likewise for coastal communities to the north.
Llyn Cowlyd Llyn Cowlyd is the deepest lake in northern Wales. It lies in the Snowdonia National Park at the upper end of Cwm Cowlyd on the south-eastern edge of the Carneddau range of mountains, at a height of above sea level. The lake is long and narrow ...
has supplied the towns of
Conwy Conwy (, ), previously known in English as Conway, is a walled market town, community and the administrative centre of Conwy County Borough in North Wales. The walled town and castle stand on the west bank of the River Conwy, facing Deganwy on ...
and
Colwyn Bay Colwyn Bay ( cy, Bae Colwyn) is a town, community and seaside resort in Conwy County Borough on the north coast of Wales overlooking the Irish Sea. It lies within the historic county of Denbighshire. Eight neighbouring communities are incorpo ...
with water since the level of the natural lake was raised by a dam in 1897. Bala and surrounding villages have been supplied by the artificially raised waters of
Llyn Arenig Fawr Llyn Arenig Fawr is a lake and reservoir located near the summit of Arenig Fawr, a mountain in North Wales. The lake's primary purpose is to supply water to the nearby town of Bala and the numerous small villages in the surrounding area. From t ...
. Elsewhere Llyn Elsi has been supplying water to
Betws-y-Coed Betws-y-coed (; '' en, prayer house in the wood'') is a village and community in the Conwy valley in Conwy County Borough, Wales, located in the historic county of Caernarfonshire, right on the boundary with Denbighshire, in the Gwydir Forest. ...
since its damming in 1914 whilst supplies to the village and to nearby
Llanrwst Llanrwst ('church or parish of Saint Grwst'; ) is a market town and community on the A470 road and the River Conwy, in Conwy County Borough, Wales, and the historic county of Denbighshire. It developed round the wool trade and became known als ...
are supplemented by water from Llyn Conwy.
Barmouth Barmouth ( cy, Abermaw (formal); ''Y Bermo'' (colloquial)) is a seaside town and community (Wales), community in the county of Gwynedd, northwestern Wales, lying on the estuary of the Afon Mawddach and Cardigan Bay. Located in the Historic coun ...
is served by Llyn Bodlyn. The height of
Llyn Cwellyn Llyn Cwellyn (''Llyn Quellyn'' in some antiquated texts) is a reservoir in North Wales which supplies drinking water to parts of Gwynedd and Anglesey. It lies on the Afon Gwyrfai in Nant y Betws between Moel Eilio and Mynydd Mawr in the north ...
was raised as it took on the role of supplying water to parts of Gwynedd and Anglesey.


HEP schemes

The establishment of an aluminium works at
Dolgarrog Dolgarrog is a village and community (Wales), community in Conwy County Borough, in Wales, situated between Llanrwst and Conwy, very close to the Conwy River. The village is well known for its industrial history since the 18th century a ...
led to construction of Dolgarrog Power Station which was supplied with water from the damming of the natural lake of
Llyn Eigiau Llyn Eigiau is a lake on the edge of the Carneddau range of mountains in Snowdonia, Conwy, Wales. The name ''Eigiau'' is thought to refer to the shoals of fish which once lived here. Early maps refer to it as ''Llynyga''. It is thought that ...
and the smaller
Coedty Reservoir Coedty Reservoir is a reservoir in Snowdonia, North Wales. It is fed by the waters of Afon Porth-llwyd which flows from Llyn Eigiau. The reservoir lies at a height of , and measures some in size. It contains brown trout. The original dam was ...
downstream of it. The latter was constructed in 1924 but the failure of the Eigiau dam in 1925 caused its destruction. It was rebuilt in 1926 and modified in 1956. Water was also sourced for this HEP scheme from
Llyn Cowlyd Llyn Cowlyd is the deepest lake in northern Wales. It lies in the Snowdonia National Park at the upper end of Cwm Cowlyd on the south-eastern edge of the Carneddau range of mountains, at a height of above sea level. The lake is long and narrow ...
, itself supplemented by a leat from a dammed
Ffynnon Llugwy Ffynnon Llugwy ( en, Llugwy spring) is a lake in the Carneddau range of mountains in Snowdonia, North Wales. It lies at a height of about and covers an area of some . It has a maximum depth of . Since the early twentieth century water has been ...
. The latter has provided a water supply for Bangor and east
Anglesey Anglesey (; cy, (Ynys) Môn ) is an island off the north-west coast of Wales. It forms a principal area known as the Isle of Anglesey, that includes Holy Island across the narrow Cymyran Strait and some islets and skerries. Anglesey island ...
since the mid 1970s. The extensive mire of Gors Goch was flooded by the raising of a dam between 1924 and 1928 to form
Llyn Trawsfynydd Llyn Trawsfynydd is a large man-made reservoir situated near the village of Trawsfynydd in Gwynedd, North Wales. With a total surface area of the reservoir is slightly more extensive than Wales's largest natural lake, Llyn Tegid at . History ...
to enable HEP at Maentwrog. Between 1965 and 1991 the reservoir was also used as a source of cooling water for the
Trawsfynydd nuclear power station Trawsfynydd nuclear power station ( cy, Atomfa Trawsfynydd) is a decommissioned Magnox nuclear power station situated in Snowdonia National Park in Gwynedd, Wales. The plant, which became operational in 1965, was the only nuclear power station in ...
. The UK’s first major pumped storage scheme was developed at
Ffestiniog Ffestiniog () is a community in Gwynedd in Wales, containing several villages, in particular the settlements of Llan Ffestiniog and Blaenau Ffestiniog. It has a population of 4,875. History Ffestiniog was a parish in Cantref Ardudwy; in 1284 ...
in 1963. It uses Llyn Stwlan, a natural tarn lake enlarged by the construction of a dam as an upper reservoir and Llyn Ystradau as a lower reservoir. Llyn Stwlan had been previously enlarged in 1898. The development during the 1970’s of the Dinorwig HEP scheme involved the damming of
Marchlyn Mawr Marchlyn Mawr reservoir is a high level lake in Snowdonia behind Elidir Fawr mountain. It is used as the high level water source for Dinorwig power station, a closed-loop pumped storage hydroelectric generating facility. It is said that nearby ...
as a top water storage facility and the use of the originally natural
ribbon lake A ribbon lake is a long and deep, finger-shaped lake, usually found in a glacial trough. As such, a ribbon lake is one of a number of glacial landscapes, including arêtes, corries, rock lips, rock basins and terminal moraines. Such a lake's fo ...
of
Llyn Peris Llyn Peris is a lake in Snowdonia, Wales, approximately 1.8 km long and situated close to the villages of Llanberis and Nant Peris, and the smaller twin of Llyn Padarn. The lake was formed glacially and is an example of a moraine-dammed la ...
as the lower reservoir for the scheme. Its capacity was increased by the removal of slate debris which had been dumped into it over decades during the operation of the Dinorwic quarry. On a smaller scale, the damming of Llyn Bodgynydd and Llyn Glangors served to provide power to the former Pandora
lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
mine just as Llyn Parc’s waters supplied power to Aberllyn lead and
zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
mine.
Llyn Mair Llyn Mair ''(Welsh for 'Mary's lake')'' is a artificial lake near Maentwrog, in Gwynedd in North Wales (grid reference ). It lies in the area of Tan-y-Bwlch, a little above Plas Tan-y-Bwlch, and is in the catchment area of the River Dwyryd. It ...
provided both a drinking supply and a source of hydro-electric power for Plas Tan-y-Bwlch from the 1890’s.


Reservoirs in South Wales

The growth in the size of towns in industrialising South Wales during the latter part of the 19th and early part of the 20th centuries necessitated the construction of numerous reservoirs for domestic water supply and for industrial use. Cardiff Corporation Waterworks opened both
Llanishen Reservoir Llanishen Reservoir ( cy, Cronfa Ddŵr Llanisien) is a Victorian reservoir in North Cardiff in Wales. The reservoir is one of the reservoirs constructed as part of the Taff Fawr scheme for supplying water to Cardiff and was completed in 1886. I ...
and
Lisvane Reservoir Lisvane Reservoir at Lisvane, Cardiff, south Wales is one of several reservoirs constructed as part of the Taff Fawr scheme for supplying water to Cardiff, completed in 1886. It is adjacent to Llanishen Reservoir and forms part of the Nant Fawr ...
in 1886. It later commissioned the construction of three reservoirs in Cwm Taf to supply water to the capital.
Beacons Reservoir Beacons Reservoir () is the northernmost of the three reservoirs in the Taff Fawr valley in South Wales. It was built by Cardiff Corporation Waterworks between 1893 and 1897, and the water is impounded by an earth dam with a clay core. Since 1 ...
was the first to take shape, between 1893–97,
Cantref Reservoir Cantref Reservoir is the middle of the three reservoirs in the Taff Fawr valley in Wales. It was built by Cardiff Corporation Waterworks between 1886 and 1892, but since 1973 has been owned by Welsh Water. It is located in the Brecon Beacons Nat ...
was built between 1886–92 and the damming of the largest of the three,
Llwyn-on Reservoir Llwyn-on Reservoir (or Llwyn Onn Reservoir) is the largest and southernmost of the three reservoirs in the Taf Fawr valley in South Wales. Cardiff Corporation Waterworks obtained an Act of Parliament in 1884 to authorise construction of the res ...
began in 1911 with the supply of water starting in the mid 1920s.
Cray Reservoir Cray Reservoir is a storage reservoir located in the Brecon Beacons National Park (named after the village of Crai) for the water supply to the city of Swansea in South Wales and was built between 1898 and 1908 by Swansea Corporation. The rese ...
was constructed between 1898-1908 to supply water to Swansea and the city council completed work on Usk Reservoir in 1955. Nearby
Neath Neath (; cy, Castell-nedd) is a market town and Community (Wales), community situated in the Neath Port Talbot, Neath Port Talbot County Borough, Wales. The town had a population of 50,658 in 2011. The community of the parish of Neath had a po ...
began to take water from
Ystradfellte Reservoir Ystradfellte Reservoir is a water storage reservoir on the Afon Dringarth in the upland area of Fforest Fawr within the Brecon Beacons National Park in South Wales. It lies just north of the village of Ystradfellte in the county of Powys at OS ...
in 1914 (1907) on completion of the rural district council’s work on the dam on the
Afon Dringarth The Afon Dringarth (or simply ''Tringarth'') is a river in Powys, Wales and wholly contained within the Brecon Beacons National Park. Its headwater streams drain the eastern slopes of Fan Dringarth (which is probably named after the river), the s ...
. Newport Corporation built
Talybont Reservoir Talybont Reservoir ( cy, Cronfa Ddŵr Tal-y-bont) is the largest stillwater reservoir in the central Brecon Beacons at . Talybont-on-Usk is downstream of the dam. Construction of the current dam started in 1931 by Newport Corporation, and in ...
between 1931-1939.
Llandegfedd Reservoir Llandegfedd Reservoir (also known as ''Llandegveth Reservoir'') is a large 174 hectare water supply reservoir and is eight miles (13 km) north of Newport in south Wales. The reservoir is very close to Pontypool, Cwmbran and Usk, with t ...
began supplying water in 1965 to
Cardiff Cardiff (; cy, Caerdydd ) is the capital and largest city of Wales. It forms a principal area, officially known as the City and County of Cardiff ( cy, Dinas a Sir Caerdydd, links=no), and the city is the eleventh-largest in the United Kingd ...
, Newport,
Pontypool Pontypool ( cy, Pont-y-pŵl ) is a town and the administrative centre of the county borough of Torfaen, within the historic boundaries of Monmouthshire in South Wales. It has a population of 28,970. Location It is situated on the Afon Lwyd ri ...
and other areas nearby. It draws its water from the
River Usk The River Usk (; cy, Afon Wysg) rises on the northern slopes of the Black Mountain (''y Mynydd Du''), Wales, in the westernmost part of the Brecon Beacons National Park. Initially forming the boundary between Carmarthenshire and Powys, it fl ...
, being pumped up from a weir above
Usk Usk ( cy, Brynbuga) is a town and community in Monmouthshire, Wales, northeast of Newport. It is located on the River Usk, which is spanned by an arched stone bridge at the western entrance to the town. Usk Castle, above the town, overlooks th ...
. Grwyne Fawr Reservoir, the only reservoir within the Black Mountains massif was completed by Abertillery and District Water Board in 1928, serving to supply water to various towns in the traditional county of Monmouthshire. A holding reservoir in
Cwmtillery Cwmtillery () (population 2011. 4800) is a ward of Abertillery. Located within the historic boundaries of Monmouthshire, it is part of the administrative area of the county borough of Blaenau Gwent, Wales. Etymology The name of the ward me ...
was constructed as a part of the scheme. Blaenycwm Reservoir to the northwest of
Brynmawr Brynmawr (; , ,) is a market town, community and electoral ward in Blaenau Gwent, Wales. The town, sometimes cited as the highest town in Wales, is situated at above sea level at the head of the South Wales Valleys. It grew with the devel ...
, was originally constructed as a water supply for
Nantyglo Ironworks Nantyglo () is a village in the ancient parish of Aberystruth and county of Monmouth situated deep within the South Wales Valleys between Blaina and Brynmawr in the county borough of Blaenau Gwent. Governance An electoral ward in the same name ...
but enlarged for public supply during the 20th century.
Llyn Brianne Llyn Brianne is a man-made lake or reservoir in the headwaters of the River Tywi in Wales. Construction The reservoir was constructed by Wimpey Construction in the late 1960s and early 1970s in order to regulate the flow in the Tywi to supp ...
was constructed in the late 1960s to provide additional water supply to South Wales via the Felindre water treatment works. The original intention was to supplement supplies of water to Swansea, Neath and Port Talbot but a subsequent extension of the trunk mains provides water up to west Cardiff.


River regulation

Rivers are an effective and cheap means of moving water from high ground to lowland areas where much of the population lives. River regulation reservoirs make use of that opportunity to store winter rainfall and release it, as needed , during drier parts of the year. This makes increased volumes of water available for abstraction down-stream, sometimes right down at the tidal limit as in the case of the River Dee. It also provides flexibility in where the downstream abstractions are made depending on demand on a day-by-day basis. River regulation reservoirs may also play a role in winter flood mitigation. Operational rules may prescribe a maximum water height at the end of Autumn to ensure that the reservoir can absorb any extreme winter rainfall events in the uplands thus mitigating high flows downstream,
Llyn Clywedog The Clywedog Reservoir ( cy, Llyn Clywedog) is a reservoir near Llanidloes, Wales on the head-waters of the River Severn. The construction of the reservoir was enabled by an Act of Parliament which asserted that ''"At certain times the flow of w ...
performs this function on the
River Severn , name_etymology = , image = SevernFromCastleCB.JPG , image_size = 288 , image_caption = The river seen from Shrewsbury Castle , map = RiverSevernMap.jpg , map_size = 288 , map_c ...
. River regulation reservoirs are marginally cheaper to construct since there is no requirement for a take-off tower or associated large volume pipe-work or aqueducts piercing the dam wall. However a number of such reservoirs have installed hydro-electric generating sets to extract power from the released water. Examples of river regulation reservoirs include
Llyn Brianne Llyn Brianne is a man-made lake or reservoir in the headwaters of the River Tywi in Wales. Construction The reservoir was constructed by Wimpey Construction in the late 1960s and early 1970s in order to regulate the flow in the Tywi to supp ...
on the
River Tywi The River Towy ( cy, Afon Tywi, ) is one of the longest rivers flowing entirely within Wales. Its total length is . It is noted for its sea trout and salmon fishing. Route The Towy rises within of the source of the River Teifi on the lower sl ...
and
Llyn Celyn Llyn Celyn () is a reservoir constructed between 1960 and 1965 in the valley of the River Tryweryn in Gwynedd, Wales. It measures roughly long by wide, and has a maximum depth of . It has the capacity to hold of water. It was originally ...
and
Llyn Brenig Llyn Brenig is a reservoir located on Denbigh Moors in North Wales. The artificial lake, which was constructed between 1973 and 1976, was created by building an embankment dam across the ''Afon Brenig'' valley. It lies at above sea level on t ...
on the River Dee. Proposals in the past have also included complex inter-river transfer schemes with, in one case, the enlargement of
Craig Goch reservoir __NOTOC__ Craig may refer to: Geology *Craig (landform), a rocky hill or mountain often having large casims or sharp intentations. People (and fictional characters) *Craig (surname) *Craig (given name) Places Scotland *Craig, Angus, aka Barony of ...
, the release of water into the River Severn via the
Afon Elan The Afon Elan ( en, River Elan) is a tributary of the River Wye which runs through the wide expanse of upland moors, traditionally known as Elenydd, in central Wales. Its valley is the Elan Valley. The name probably arises from ''elain'' meani ...
and then a pumped transfer into the headwaters of the
River Thames The River Thames ( ), known alternatively in parts as the The Isis, River Isis, is a river that flows through southern England including London. At , it is the longest river entirely in England and the Longest rivers of the United Kingdom, se ...
. Despite the benefits of such regulation schemes, they have been shown to have a number of adverse
environmental impacts Environmental issues are effects of human activity on the biophysical environment, most often of which are harmful effects that cause environmental degradation. Environmental protection is the practice of protecting the natural environment on t ...
. When releases are made they are typically from the reservoir bottom water drawing from the
hypolimnion The hypolimnion or under lake is the dense, bottom layer of water in a thermally- stratified lake. The word hypolimnion is derived from the Greek "limnos" meaning "lake". It is the layer that lies below the thermocline. Typically the hypolimnio ...
which is often very cold, acidic, iron rich and
anoxic The term anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts: * Anoxic waters, sea water, fresh water or groundwater that are depleted of diss ...
. The change in flow rate can also be very rapid which may be a serious hazard for water users who may have no warning of a very sudden increase in flow. Aquatic animals have also been shown to be adversely affected with spawning behaviour and
smoltification Smoltification (also known as Parr-Smolt transformation) is a complex series of physiological changes where young salmonid fish adapt from living in fresh water to living in seawater. Physiological changes during smoltification include modified bod ...
of
salmon Salmon () is the common name for several list of commercially important fish species, commercially important species of euryhaline ray-finned fish from the family (biology), family Salmonidae, which are native to tributary, tributaries of the ...
affected below Llyn Brianne for example. There may also be unexpected benefits. The operational rules for Llyn Celyn include a specific allocation of releases for recreational purposes to support competitive
whitewater Whitewater forms in a rapid context, in particular, when a river's gradient changes enough to generate so much turbulence that air is trapped within the water. This forms an unstable current that froths, making the water appear opaque and ...
sports in the
Afon Tryweryn The Tryweryn is a river in the north of Wales which starts at Llyn Tryweryn in the Snowdonia National Park and after joins the river Dee at Bala. One of the main tributaries of the Dee, it was dammed in 1965 to form Llyn Celyn, drowning the ...
below the reservoir.
Canolfan Tryweryn Canolfan Tryweryn is the National White Water Centre for Wales, and is based near Bala in north Wales. It developed the first commercial white water rafting operation in the UK in 1986, and since then has grown to become the largest and on ...
, the national white-water centre for Wales was constructed on the river and maintains the infrastructure of overhead gates etc for all white-water sports which also benefit from the routine releases of water to support river flow, mostly in the summer months.


Notable reservoirs

*
Llyn Trawsfynydd Llyn Trawsfynydd is a large man-made reservoir situated near the village of Trawsfynydd in Gwynedd, North Wales. With a total surface area of the reservoir is slightly more extensive than Wales's largest natural lake, Llyn Tegid at . History ...
is the only reservoir or lake in the United Kingdom to have provided a source of cooling water for a
nuclear power station A nuclear power plant (NPP) is a thermal power station in which the heat source is a nuclear reactor. As is typical of thermal power stations, heat is used to generate steam that drives a steam turbine connected to a generator that produces elec ...
*
Llyn Brianne Llyn Brianne is a man-made lake or reservoir in the headwaters of the River Tywi in Wales. Construction The reservoir was constructed by Wimpey Construction in the late 1960s and early 1970s in order to regulate the flow in the Tywi to supp ...
has the tallest dam in the UK *
Llyn Clywedog The Clywedog Reservoir ( cy, Llyn Clywedog) is a reservoir near Llanidloes, Wales on the head-waters of the River Severn. The construction of the reservoir was enabled by an Act of Parliament which asserted that ''"At certain times the flow of w ...
has the tallest concrete dam in the UK


Safety and failures

It was, in part, the failure of the
Llyn Eigiau Llyn Eigiau is a lake on the edge of the Carneddau range of mountains in Snowdonia, Conwy, Wales. The name ''Eigiau'' is thought to refer to the shoals of fish which once lived here. Early maps refer to it as ''Llynyga''. It is thought that ...
dam, and consequent collapse of the dam of a second reservoir (Coedty) downstream, in the then
Caernarvonshire , HQ= County Hall, Caernarfon , Map= , Image= Flag , Motto= Cadernid Gwynedd (The strength of Gwynedd) , year_start= , Arms= ''Coat of arms of Caerna ...
(modern
Gwynedd Gwynedd (; ) is a county and preserved county (latter with differing boundaries; includes the Isle of Anglesey) in the north-west of Wales. It shares borders with Powys, Conwy County Borough, Denbighshire, Anglesey over the Menai Strait, and C ...
) in 1925 with the loss of 16 lives in the village of
Dolgarrog Dolgarrog is a village and community (Wales), community in Conwy County Borough, in Wales, situated between Llanrwst and Conwy, very close to the Conwy River. The village is well known for its industrial history since the 18th century a ...
which led to the enactment of the Reservoirs (Safety Provisions) Act in 1930. Under this legislation, all reservoir owners in Wales and England were required to have them inspected by a suitably qualified civil engineer, if the capacity exceeded five million gallons (22,700 cubic metres). The Reservoirs Act of 1975 placed further duties upon both owners and local authorities in respect of the safety of those with a capacity of more than 25,000 cubic metres. The
Environment Agency The Environment Agency (EA) is a non-departmental public body, established in 1996 and sponsored by the United Kingdom government's Department for Environment, Food and Rural Affairs, with responsibilities relating to the protection and enha ...
assumed safety responsibilities in September 2004 and in 2013 the duties were transferred from the
Environment Agency Wales Environment Agency Wales () was a Welsh Government sponsored body that was part of the Environment Agency of England and Wales from 1996 to 2013. Its principal aims were to protect and improve the environment in Wales and to promote sustainab ...
to
Natural Resources Wales Natural Resources Wales ( cy, Cyfoeth Naturiol Cymru) is a Welsh Government sponsored body, which became operational from 1 April 2013, when it took over the management of the natural resources of Wales. It was formed from a merger of the Count ...
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References

*''The Lakes of Eryri'', by Geraint Roberts, Gwasg Carreg Gwalch, 1985 {{reflist


See also

*
List of lakes of Wales This is a list of lakes in Wales, including those created as reservoirs. The names of most lakes in Wales start with the word "''Llyn''", which is Welsh for "''lake''". Except where otherwise referenced, all lakes listed here are named on the rel ...
Reservoirs in Wales