Lochs and pools
Lochs and pools
Orkney’s lochs and pools may be described as either upland or lowland. The upland lochs, or black lochs, exist on peat and being composed largely of rainwater are nutrient-poor. The lowland lochs on the other hand are fed by burns that pass through surrounding farmland resulting in nutrient-rich waters.
Around Scapa Flow, the upland lochs occur exclusively on Hoy. There are numerous small black lochs on most of the island’s hills with especially high concentrations on Genie Fea, Withi Gill and Bailie Fea. Many of them are colourful with floating mats of bogbean. Red-throated divers frequently nest on the sides of these lochs and the loch’s remoteness provides security while being close enough to the diver’s feeding grounds in Scapa Flow. There are a handful of larger peaty lochs most notably Sandy Loch, the Water of Hoy, the Water of the Wicks, Sands Water, Hoglinns Water and the largest of them all Heldale Water. These bigger bodies of water are attractive to gatherings of great skuas which come to the lochs to bathe and preen.
Unlike the upland lochs, the nutrient-rich lochs of the lowlands are not as numerous. Bordering Scapa Flow they range from the Loch of Stenness in the north via the Loch of Ayre in Holm, Echna Loch on Burray to the Dam of Hoxa on South Ronaldsay. Fringing these lochs are rushes and wildflowers such as yellow flag, water mint and meadowsweet. The abundant plant, insect and fish life provides a long-lasting supply of food in the autumn, winter and spring to wildfowl such as wigeon, teal and goldeneyes. In the lush lochside vegetation mute swans, mallards, tufted ducks and moorhens nest.
In bygone times three of these lochs would have been part of Scapa Flow; now all of them are freshwater and separated from the sea by a narrow strip of land known as an ayre. The exception is the Loch of Stenness, the second largest saline lagoon in Britain; in reality it is an arm of Scapa Flow in which harbour seals are frequently observed and mussel shells can be found along the loch shore.