The Landscape and Geology

The rocks of Scapa Flow were formed 400 million years ago when Orkney was covered by Lake Orcadie, a freshwater lake. Layers of sediment – sand, mud and silt, were laid down in the bottom of the lake and compressed over millions of years to form the layered mudstones and sandstones, which we see today. These rocks have been shaped by glaciers, and scoured out by the ice to form the deep basin and natural harbour that is Scapa Flow. The deepest part of the Flow, the Bring Deeps, is thought to be an old glacial lake and is about 60m deep. Wind and sea have helped to erode the rocks to form high cliffs, rocky shorelines, sheltered coves and wide sandy bays which surround the Flow. The main entrances are to the south, through Switha and Hoxa Sounds and to the west through Hoy Sound.

The Nature

The varied coastline, the sheltered bays, and the marine environment itself support a wonderful range of wildlife and plants.

Beneath the surface of the waters is a whole world to explore. Wrecks from the World Wars support a great variety of sea life – some with strange names like 'dead men's fingers' and others more familiar like sea anemones, sponges and sea urchins. The sandy and muddy seabed is less visited by scuba divers but is still home to a variety of creatures including scallops and clams and delicate sea fans.

Seals, porpoises and dolphins frequent the waters of the Flow, with harbour porpoise being the most regular visitors. Even large whales occasionally visit but sometimes find it hard to find their way out again. Six sperm whales were trapped in the Flow for several weeks in 1993. They had to be herded to the entrance by a fleet of 17 boats arranged in a horseshoe formation.

Usually it is the seals that visitors spot, either swimming along the coast or hauled out on rocks or sand like sunbathers. Up to 2,000 common seals enjoy the sheltered waters of the area.

You do not have to be a diver to explore the Flow’s sea life. Sea shells like the delicate thin tellin and the 'spoot' or razor shell get washed up on beaches such as Waulkmill and are easy to find. At a good low tide the rocky shores of the Bu and the Holm of Houton have an abundance of crabs, sea anemones, starfish and rock pool fish such as the slippery butterfish. The sheltered waters of the Flow are important to birds, especially in the winter, when escaping from the open sea must seem like a good idea! It is an internationally important wintering area for great northern divers and long-tailed duck.

Shore birds enjoy feeding in the sheltered bays, probing for worms and shells in the sand or hunting for food in seaweed or under stones. Common birds to spot are oystercatcher, curlew, turnstone, ringed plover and purple sandpiper.

In the summer the Flow is a good feeding ground for gulls, terns and cliff-nesting birds such as common guillemots and razorbills.

You cannot help but enjoy the summer wild flowers along the coasts. Plants like sea pinks and spring squill grow right on the cliff edge, along with dwarf willow, a low growing tree perfectly adapted to Orkney’s windy climate. Behind a shingle spit at the head of Waulkmill Bay lies an extensive area of salt marsh, which is covered by the sea at high tide. It has a distinctive array of very salt tolerant plants such as sea milkwort and sea arrow grass. Remnants of once widespread heathland can be seen around the Flow, especially at Hobbister, where the vegetation is dominated by ling and bell heather, and [is] colourful with herbs such as tormentil. There is always something to see around the shores of Scapa Flow throughout the year.