Scapa Flow has been as an important haven for over 1000 years. This stretch of water, very roughly 20km from east to west and 15km from north to south lies, atoll-like, within the shelter of the surrounding Orkney islands. The result is one of the largest natural harbours in the world.

Today's Scapa Flow is home to a major oil terminal at Flotta. Here up to 10% of the UK's oil arrives by pipe from North Sea oilfields before being transferred to tankers for shipment around the world. Traffic through these busy waters is overseen by the Scapa Flow Control Centre at Scapa Bay, a mile south of Kirkwall.

And with a flat bottom at depths of between 60 and 150 feet, an absence of strong currents, and an abundance of wrecks, it is also the centre of a major tourist diving industry, based primarily at Stromness and on Burray and South Ronaldsay. About 15 dive boats cater for up to 20,000 divers who come to Orkney each year to dive Scapa Flow.

Though no evidence remains, Scapa Flow was probably used for fishing by the builders of Maes Howe, 5000 years ago. But it first came into recorded history with the Vikings. Their world extended from Iceland to Ireland, and from Scandinavia to North Eastern England, and Orkney lay at its centre. The name comes from the Old Norse, Skalpeid-floi, or Bay of the Long Isthmus.