Scapa Flow is very popular because of the various wrecks that were deliberately sunk here during the wars - some as part of the scuttling of the German Fleet and some to block the movement of U-Boats, while the British Naval Fleet was anchored here. These later ships were often known as "Block Ships" and some stood just above the water line. There was one off Graemsay right up until a few years ago when it sank below the water line. More on the ships here and here. Any ship where there was a loss of life, such as the "Royal Oak" are war graves and diving is forbidden.
The film starts with the journey of a group of divers last September from Germany, arriving in Scrabster then across to Stromness, which is the heart of the tourism diving industry in Orkney. There is some film down among the wrecks, lovely undersea flora and fish; a visit to the Scapa Flow Museum; and then a stunning few minutes footage of diving with seals!