Llyn Eigiau is a lake on the edge of the Carneddau

Carneddau

The Carneddau , are a group of mountains in Snowdonia, Wales. It includes the largest contiguous areas of high ground in Wales and England, as well as six or seven of the highest peaks in the country—the Fourteen Peaks...

 range of mountains in Snowdonia

Snowdonia

Snowdonia is a region in north Wales and a national park of in area. It was the first to be designated of the three National Parks in Wales, in 1951.-Name and extent:...

, North Wales

North Wales

North Wales is the northernmost unofficial region of Wales. It is bordered to the south by the counties of Ceredigion and Powys in Mid Wales and to the east by the counties of Shropshire in the West Midlands and Cheshire in North West England...

.

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 a small number of Arctic char

Arctic char

Arctic char or Arctic charr is both a freshwater and saltwater fish in the Salmonidae family, native to Arctic, sub-Arctic and alpine lakes and coastal waters. No other freshwater fish is found as far north. It is the only species of fish in Lake Hazen, on Ellesmere Island in the Canadian Arctic...

 exist in the lake (as they do in neighbouring Llyn Cowlyd

Llyn Cowlyd

Llyn Cowlyd is the deepest lake in North Wales. It lies in the Snowdonia National Park on the edge of the Carneddau range of mountains, at a height of above sea level. The lake is long and narrow, measuring nearly long and about a third of a mile wide, and covers an area of...

) after they were transferred here from Llyn Peris

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. The lake was formed glacially and is an example of a moraine-dammed lake. Llyn Peris is named after Saint Peris, an early Christian saint of whom little is known...

, and certainly it is one of the few lakes in Wales to have its own natural brown trout

Brown trout

The brown trout and the sea trout are fish of the same species....

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In 1911 a dam ¾ mile long and 35 feet (10.7 m) high was built across part of its eastern side to supply water for the power station at Dolgarrog

Dolgarrog

Dolgarrog is a small village in the Conwy County Borough in North 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 and the Eigiau dam disaster, which occurred in 1925...

, which in turn provided power for the adjacent aluminium

Aluminium

Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

 works. Materials for the dam were transported along the newly-laid Eigiau Tramway

Eigiau Tramway

The Eigiau Tramway might refer to the Eigiau Quarry Tramway or to the Eigiau Reservoir Tramway.- Eigiau Quarry Tramway :The Eigiau Quarry Tramway was a narrow gauge mile-long horse-powered tramway which operated from c1863 to c1888 and served the Eigiau slate quarry [ref SH702635], near Llyn Eigiau...

, which ran from Dolgarrog and utilized the route of the former Cedryn Quarry Tramway

Cedryn Quarry Tramway

The Cedryn Quarry Tramway was an industrial narrow gauge railway that connected the slate quarries at Cedryn and Cwm Eigiau to the quays at Dolgarrog in the Conwy valley.- History :...

. The original contractor pulled out of the construction, alleging corner cutting, and indeed on 2 November 1925, following 26 inches (660.4 mm) of rain in just five days, the dam broke. The water flowed down to Coedty reservoir

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....

, also causing that to burst, and millions of gallons of water flowed down into the village of Dolgarrog

Dolgarrog

Dolgarrog is a small village in the Conwy County Borough in North 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 and the Eigiau dam disaster, which occurred in 1925...

, causing the loss of 17 lives. A new power station was built at Dolgarrog in 1925.
A study of the dam today shows that indeed the foundations were quite insufficient, and large lumps of unmixed cement can also be seen. The dam material that can be seen through existing holes is flaky and tends to break away easily.

Today the lake covers an area of about 120 acre (0.4856232 km²), and has a depth of about 32 feet (9.8 m). After the construction of the dam its area would have been twice this.

Water is fed into Llyn Eigiau by a tunnel from the stream below Llyn Dulyn

Llyn Dulyn

Llyn Dulyn is a lake on the edge of the Carneddau range of mountains in Snowdonia, North Wales.The lake covers an area of only , yet is extremely deep - it reaches to a depth of 189'...

, and another larger tunnel takes water from Llyn Eigiau to Llyn Cowlyd

Llyn Cowlyd

Llyn Cowlyd is the deepest lake in North Wales. It lies in the Snowdonia National Park on the edge of the Carneddau range of mountains, at a height of above sea level. The lake is long and narrow, measuring nearly long and about a third of a mile wide, and covers an area of...

.

The main feeder of Llyn Eigiau is Afon Eigiau

Afon Eigiau

Afon Eigiau is a small river in the Carneddau mountains in Snowdonia, North Wales, which flows down Cwm Eigiau and into Llyn Eigiau.It is fed by smaller streams which flow down the slopes of neighbouring Foel Grach, Carnedd Llywelyn and Pen yr Helgi Du....

, a small river which flows down Cwm Eigiau.

The outflow from Llyn Eigiau is called Afon Porth-llwyd

Afon Porth-llwyd

Afon Porth-llwyd is a river in Snowdonia, North Wales. It flows from Llyn Eigiau on the south-eastern edge of the Carneddau range to join the river Conwy.Its waters are trapped at Coedty reservoir before flowing down to pass under Pont Newydd in Dolgarrog...

, and this flows via Coedty reservoir

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....

 before passing under Pont Newydd in Dolgarrog. This then flows into the River Conwy

River Conwy

The River Conwy is a river in north Wales. From its source to its discharge in Conwy Bay it is a little over long. "Conwy" is sometimes Anglicized as "Conway."...

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Although private vehicles are not permitted access to the lake itself, there is a carpark within walking distance, approx. half a mile from the dam and which is reached by road from the B5106 at Tal-y-bont

Tal-y-bont, Conwy

Tal-y-Bont is a small village in Conwy County Borough, Wales. It lies in the Conwy Valley in North Wales, west of the River Conwy, on the B5106 road, six miles from Conwy to the north, and six miles from Llanrwst to the south....

, in the Conwy valley. The road passes through Llanbedr-y-Cennin

Llanbedr-y-Cennin

Llanbedr-y-Cennin is a small village in Conwy county borough, Wales.It lies in the foothills on the western side of the Conwy valley, in North Wales. The river Conwy runs through the valley, running into the sea to the north, at the town of Conwy, which is about five miles north of the village. ...

and thereafter becomes a narrow lane as it goes over the hills towards the lake. Along this lane there are some public footpaths signposted, with stiles to access them over the old dry-stone walls that run along parts of the lane.