Scapa Flow's stunning wildlife, in the air and sea and on the shores, makes it a mecca for nature lovers.
Common and grey seals abound and can be seen lounging on skerries at low tide or swimming near the shore.
Resident porpoises are commonly seen, particularly in Hoxa Sound, and whales pass by every year – 19 species have been recorded, including orcas (killer whales), causing much excitement. Basking shark sightings are increasing.
There are so many habitats around the shores and isles of Scapa Flow that there is a wide diversity of bird species, both resident and visiting. The largest sheltered area of sea in Britain has some of Britain's most important colonies.
Cliffs are home to large numbers of seabirds including kittiwake, fulmar, puffin and the rare storm petrel. On the shore are oystercatcher, curlew, eider duck and black guillemot and many more.
Rock pools provide habitat for seaweed and algae which in turn provide food for marine organisms and animals such as anemones, starfish, shellfish, molluscs, crab and squat lobster.
The seabed is home to many fish species, shellfish, algae and burrowing animals which are vital food for the birds and sea mammals.
There is a whole world under the water which is explored every year by thousands of visiting divers. Some are interested in the natural world of animals and plants below the surface but most are drawn to Scapa Flow to explore the wrecks of the scuttled German High Sea Fleet or to look for undiscovered wartime boats and aircraft.
Every year there are new finds and underwater archaeology is growing in popularity. However archaeologists are searching for more ancient evidence beneath the waves including prehistoric sites. Much of Orkney's previous land has been lost through rising tides and submerged landscapes are the focus of much study, as is the monitoring of coastal erosion and change.
On the surface of the Flow modern ships continue to use its safe waters and deep water anchorage including ferries, cruise ships and oil tankers. The harbour is one of the principal locations in Europe for ship-to-ship transfers of crude and fuel oils.
Fishing and creel boats reap the harvest of the sea. Leisure craft including yachts and traditional Orkney yoles enjoy Scapa Flow for recreation and regattas, while dive boats take parties out.
And the former naval base at Lyness has a future life as a centre for building, storing and servicing marine renewable energy devices.
A network of lighthouses, beacons and buoys protect Scapa Flow from shipping hazards. The famous Stevenson family designed many of Orkney's lighthouses including Cantick Head on Hoy and both Hoy Sound High and Hoy Sound Low on Graemsay. There are other lighthouses and smaller lights on Cava, the Barrel of Butter and Hoxa Head, South Ronaldsay.
© Catherine Turnbull