Llyn Cefni is a small

reservoir A reservoir (; ) is an enlarged lake behind a dam, usually built to water storage, store fresh water, often doubling for hydroelectric power generation. Reservoirs are created by controlling a watercourse that drains an existing body of wa ...

in the centre of

Anglesey Anglesey ( ; ) is an island off the north-west coast of Wales. It forms the bulk of the Principal areas of Wales, county known as the Isle of Anglesey, which also includes Holy Island, Anglesey, Holy Island () and some islets and Skerry, sker ...

Wales Wales ( ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by the Irish Sea to the north and west, England to the England–Wales border, east, the Bristol Channel to the south, and the Celtic ...

which is managed by

Welsh Water Welsh may refer to: Related to Wales * Welsh, of or about Wales * Welsh language, spoken in Wales * Welsh people, an ethnic group native to Wales Places * Welsh, Arkansas, U.S. * Welsh, Louisiana, U.S. * Welsh, Ohio, U.S. * Welsh Basin, during t ...

and Hamdden Ltd, while the fishery is managed by the Cefni Angling Association. The reservoir is located just northwest of the island's county town of

Llangefni ; ) is the county town of Anglesey in Wales. At the 2011 census, Llangefni's population was 5,116, making it the second-largest town in the county and the largest on the island. The community includes the village of Rhosmeirch. Location The ...

History

During

World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

, a water scheme was devised for the town of

in central Anglesey. It involved water from a local source being pumped to two settling tanks in the Dingle part of the town. From here the water was pumped across the river to a reservoir and water tower, on the site of the present Pennant Estate. These arrangements became redundant with the building of the Cefni Reservoir, which was completed in 1951, but the settling tanks and pumping station survive in Llangefni to this day. The new scheme was designed to supply most of the water needs for the people of Anglesey for the foreseeable future.

Geography

The

Afon Cefni Afon Cefni is one of the major rivers on the island of Anglesey, Wales. It is long. Its source is near to the village of Capel Coch, before flowing through Bodffordd and into Llyn Cefni in the centre of the island. It continues to run south ...

is one of the main rivers of Anglesey. It was dammed about northwest of Llangefni, just below the confluence of the tributary from

Tregaian Llanddyfnan is a village and community in Anglesey, Wales, located north east of Llangefni, north west of Menai Bridge and west of Beaumaris. Description The community includes the villages of Capel Coch, Ceint, Llanddyfnan, Llangwyllog, ...

with other streams flowing from the northwest, and the reservoir has a catchment area of about . The reservoir is fed by two main streams, the Afon Frogwy entering from the west and the Afon Erddreiniog from the north east end. With a maximum length of and a total water surface area of , Llyn Cefni is the second largest body of water on the island after

Llyn Alaw Llyn Alaw (meaning: ''Lily Lake'') is a man-made reservoir on Anglesey, North Wales managed by Dŵr Cymru Welsh Water. It is a shallow lake and was built in 1966. It is a Site of Special Scientific Interest and a destination for overwintering b ...

, also a reservoir. There is a

dam A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, aqua ...

on the south-east edge of the reservoir, next to which is a car park. The northeastern end of the reservoir and the immediate surrounding area have been designated as a

nature reserve A nature reserve (also known as a wildlife refuge, wildlife sanctuary, biosphere reserve or bioreserve, natural or nature preserve, or nature conservation area) is a protected area of importance for flora, fauna, funga, or features of geologic ...

, and as a further measure of conservation, a plantation of trees runs along its north shore. The tracks of the

Anglesey Central Railway The Anglesey Central Railway (Welsh: ''Lein Amlwch'', ''Amlwch Line'') was a standard-gauge railway in Anglesey, Wales, connecting the port of Amlwch and the county town of Llangefni with the North Wales Coast Line at Gaerwen. Built as an in ...

, although no longer used, still run over an embankment which crosses the water. The reservoir is easily accessible from Llangefni, as well defined paths run from the town through the local nature reserve, The Dingle, one of the few ancient woodland sites on the island. It can also be accessed by the Lôn Las Cefni cycleway which follows the Afon Cefni from The Dingle and divides at the dam. In the summer of 2011, toxic

blue-green algae Cyanobacteria ( ) are a group of autotrophic gram-negative bacteria that can obtain biological energy via oxygenic photosynthesis. The name "cyanobacteria" () refers to their bluish green (cyan) color, which forms the basis of cyanobacteria' ...

were found in the reservoir and visitors were advised to avoid contact with the water.

References

{{authority control Cefni