St Mary's Loch is the largest natural loch

Loch

Loch is the Irish and Scottish Gaelic word for a lake or a sea inlet. It has been anglicised as lough, although this is pronounced the same way as loch. Some lochs could also be called a firth, fjord, estuary, strait or bay...

 in the Scottish Borders

Scottish Borders

The Scottish Borders is one of 32 local government council areas of Scotland. It is bordered by Dumfries and Galloway in the west, South Lanarkshire and West Lothian in the north west, City of Edinburgh, East Lothian, Midlothian to the north; and the non-metropolitan counties of Northumberland...

, and is situated on the A708 road between Selkirk and Moffat

Moffat

Moffat is a former burgh and spa town in Dumfries and Galloway, Scotland, lying on the River Annan, with a population of around 2,500. The most notable building in the town is the Moffat House Hotel, designed by John Adam...

, about 72 kilometres (44.7 mi) south of Edinburgh

Edinburgh

Edinburgh is the capital city of Scotland, the second largest city in Scotland, and the eighth most populous in the United Kingdom. The City of Edinburgh Council governs one of Scotland's 32 local government council areas. The council area includes urban Edinburgh and a rural area...

. It is 5 kilometres (3.1 mi) long and 1 kilometre (0.621372736649807 mi) wide, and was created by glacial action during the last ice age

Ice age

An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...

. The loch is fed by the Megget Water

Megget Water

Megget Water is a river in the Scottish Borders area of Scotland, in the former Selkirkshire. The Water rises at Broad Hill, passes through Megget Reservoir and empties into St Mary's Loch...

, which flows in from the Megget Reservoir

Megget Reservoir

Megget Reservoir is a man-made water body in Ettrick Forest, in the Scottish Borders. The reservoir is held back by the largest earth dam in Scotland. The reservoir collects water from the Tweedsmuir Hills, which is then conveyed via pipelines to Edinburgh...

, and is the source of the Yarrow Water, which flows east from the loch to merge with the Ettrick Water above Selkirk.

The loch takes its name from a church dedicated to St Mary which once stood on its northern shore, although only the burial ground is now visible. Local legend has it that the loch has no bottom, and it is reputed to be the coldest loch in Scotland. Immediately upstream from St Mary's Loch is the smaller Loch of the Lowes. Between the two is Tibbie Shiel's Inn, an 18th-century coaching inn, which was frequented by the Border poet James Hogg

James Hogg

James Hogg was a Scottish poet and novelist who wrote in both Scots and English.-Early life:James Hogg was born in a small farm near Ettrick, Scotland in 1770 and was baptized there on 9 December, his actual date of birth having never been recorded...

 (1770–1835). A statue of Hogg is located close to the inn. The Southern Upland Way

Southern Upland Way

Opened in 1984, the Southern Upland Way is a coast to coast walk in Scotland between Portpatrick in the west and Cockburnspath in the east....

 and Sir Walter Scott Way

Sir Walter Scott Way

The Sir Walter Scott Way is a long distance path in the Scottish Borders of Scotland, in memory of Sir Walter Scott, of one of Scotland's greatest writers.-The Way:...

 long-distance walking routes both pass the shores of the loch. The small settlement of Cappercleuch

Cappercleuch

Cappercleuch is a settlement on the A708, at St. Mary's Loch in the Scottish Borders area of Scotland, in the former Selkirkshire.Places nearby include Bowerhope Law, Craigierig, Deer Law, the Dryhope Tower, Ettrickbridge, the Ettrick Forest, the Megget Reservoir, the Megget Water, Mountbenger, the...

is located at the north-west corner of the loch.