Llyn Mair

{{Use dmy dates|date=November 2019}}

{{Infobox body of water

| name = Llyn Mair

| image = Llyn Mair. - geograph.org.uk - 235172.jpg

| caption = Looking towards Coed Llyn Y Garnedd

| image_bathymetry =

|pushpin_map=Wales Gwynedd

| caption_bathymetry =

| location = North Wales

| coords = {{coord|52.951|N|4.004|W|region:GB_type:waterbody_source:enwiki-osgb36(SH652412)|display=inline,title}}

| type = artificial lake

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| basin_countries = United Kingdom

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| area = {{convert|14|acre|ha|abbr=on}}

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{{langnf|cy|Llyn Mair|Mary's lake|italic=no}} is a {{convert|14|acre|ha|adj=on}} artificial lake near Maentwrog, in Gwynedd in North Wales (grid reference {{gbmappingsmall|SH652412}}). 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 was created by William Edward Oakeley (of Plas Tan-y-bwlch) as a 21st birthday present for his daughter Mair and as a water supply. It was built in 1889, and the nearby smaller Llyn Hafod-y-Llyn dates from the same period.{{cite web |url=http://www.eryri-npa.gov.uk/visiting/walking/leisure-walks/dyffryn-maentwrog-and-llyn-mair-footpaths |title=Dyffryn Maentwrog and Llyn Mair Footpaths |publisher=Snowdonia National Park |accessdate=29 September 2016 |archive-url=https://web.archive.org/web/20161001201935/http://www.eryri-npa.gov.uk/visiting/walking/leisure-walks/dyffryn-maentwrog-and-llyn-mair-footpaths |archive-date=1 October 2016 |url-status=dead }}

Plas Tan y Bwlch is thought to be the first house in North Wales with electric lighting powered from its own hydro-electric station, which was commissioned in the 1890s. A pipeline from the lake fed water to a Pelton wheel, which was located in a small power house on the hillside immediately behind the house. It ceased to operate soon after 1928, when the public hydro-electric power station at Maentwrog began supplying the area.{{cite web|url=http://www.eryri-npa.gov.uk/study-centre/history |title=The History of Plas Tan y Bwlch |publisher=Eryri-npa.gov.uk |accessdate=29 September 2016}} In June 2013 a new hydro-scheme, costing £420,000, and similarly tapping the water from Llyn Mair, was opened. The water falls 60m to the turbine, and the scheme is expected to meet most of the Plas' electricity needs.{{cite web |url=http://snowdonia-society.org.uk/archive/news.php?n_id=431 |title=Power to the Plas |publisher=Snowdonia Society |accessdate=29 September 2016 |archive-url=https://web.archive.org/web/20161003060227/http://snowdonia-society.org.uk/archive/news.php?n_id=431 |archive-date=3 October 2016 |url-status=dead }}

The lake is set alongside the B4410 road, a minor road linking the hamlet of Rhyd. The position of the lake bordered with ancient oak woods and its tranquil appearance makes this a popular picnic site for visitors, and it is also a starting point for a number of local country walks. There is some limited parking available just off the road.

The narrow gauge Ffestiniog Railway runs through the woods above the lake, and Tan-y-Bwlch railway station can be reached on foot from the lake.

The lake also has a notable echo because of the shape of the surrounding hills.

File:TanyBwlchLB02.JPG