Vasa Loch is a brackish lagoon

Lagoon

A lagoon is a body of shallow sea water or brackish water separated from the sea by some form of barrier. The EU's habitat directive defines lagoons as "expanses of shallow coastal salt water, of varying salinity or water volume, wholly or partially separated from the sea by sand banks or shingle,...

 in southwestern Shapinsay

Shapinsay

Shapinsay is one of the Orkney Islands off the north coast of mainland Scotland. There is one village on the island, Balfour, from which roll-on/roll-off car ferries sail to Kirkwall on the Orkney Mainland...

, Orkney Islands

Orkney Islands

Orkney also known as the Orkney Islands , is an archipelago in northern Scotland, situated north of the coast of Caithness...

. (Ordnance, 2002) This water body has been shown on early maps of the island in a very similar shape and size to its current geometry, separated from the North Sea

North Sea

In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively...

 by a narrow strip of raised beach

Raised beach

A raised beach, marine terrace, or perched coastline is an emergent coastal landform. Raised beaches and marine terraces are beaches or wave-cut platforms raised above the shore line by a relative fall in the sea level ....

.(Masters, 1840) Vasa Loch is fed by small rivulets and upland springs that rise on the western part of the island's western spur. pH

PH

In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

 levels of the 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...

 are strongly alkaline, in the range of 10.15. (Hogan, 2006)

Geology

The particular landform

Landform

A landform or physical feature in the earth sciences and geology sub-fields, comprises a geomorphological unit, and is largely defined by its surface form and location in the landscape, as part of the terrain, and as such, is typically an element of topography...

 associated with Vasa Loch is an ayre

Ayre (landform)

An ayre is a name often applied to shingle beaches in Orkney and Shetland. The term is derived from the Old Norse wordfor a shingle beach - "eyrr" - and may be applied to ordinary beaches, to cliff-foot beaches to spits, bars and tombolos, but only if formed of shingle. It is sometimes wrongly...

, derived from the Old Norse

Old Norse

Old Norse is a North Germanic language that was spoken by inhabitants of Scandinavia and inhabitants of their overseas settlements during the Viking Age, until about 1300....

word used to depict a lake which is only separated by a narrow strip of low lying land from the sea itself.(Shapinsay)