The Sea Lochs: Scotland's Drowned West Coast

Each major claim carries one of three labels. established means supported by primary records, official bodies or several independent reliable sources. shared means the core fact is sound but sources disagree on details, dates or interpretation. traditional means widely repeated but not traceable to a primary or independent source.

The weakest numbers here are lengths. Coastline length depends on the scale of the map used to measure it, so official figures are explicitly estimates. Counts of sea lochs depend on what is counted as a separate loch. The age of Loch Morar's basin is also uncertain: popular accounts say "about 10,000 years", but that is when the ice left; the basin itself was deepened over many glaciations.

Fjords by another name

established A sea loch is a long inlet of the sea carved by glaciers. Marine scientists describe Scotland's sea lochs, and Ireland's sea loughs, as glacially formed inlets, also known as fjords or fjards, that are typically elongate, deepened by glacial action and little influenced by fresh water. Many have narrows and sills, ridges of rock or glacial debris near the mouth or along their length, that divide the loch into a series of basins.

established The pattern is a western one. The west coast in particular is heavily indented with fjord-like sea lochs. Around 200 named sea lochs are listed for Scotland. Loch Fyne in Argyll is the longest, running 65 kilometres inland from the Sound of Bute.

established The process is the same one that made the fjords of Norway. During the ice ages, glaciers flowing west from the Highlands followed existing valleys and lines of weakness in the rock and ground them deeper, often far below sea level. When the ice melted, the sea flooded the deepest troughs. What were glens became arms of the sea, and many of the ridges between them became peninsulas and islands.

A coast longer than it looks

shared Because the coast is so indented, Scotland's coastline is very long for a country of its size. The Scottish Government's marine directorate gives an estimate of 18,743 kilometres, measured along the line of mean high water springs from Ordnance Survey data. It stresses that all published figures are estimates, because the length of a crinkled coast depends on the size of the ruler: the finer the measurement, the longer the coast. Other references give figures as low as 11,800 kilometres. Scotland has over 900 islands, of which 118 are inhabited.

established The sea is also deep close inshore. A depth of 324 metres was observed in the Inner Sound, between Raasay and the mainland, in 1943, and was long believed to be the deepest water around the UK.

Loch Morar: the fjord that lost the sea

established Loch Morar, between Mallaig and Arisaig in Lochaber, began as a sea loch in all but name. Ice overdeepened a valley along an east–west line of weakness in the rock. NatureScot gives its depth as 310 metres, making it the deepest of all Scotland's lochs, and it is the deepest body of fresh water in the British Isles.

established What separates it from the sea is a rock sill at its western end. After the ice melted, the land rose as the weight of ice was removed, and the sill was lifted above sea level. The loch's surface now stands only 9 metres above the sea. Its outflow, the River Morar, is just a few hundred metres long, one of the shortest rivers in the British Isles. A fan of sand and gravel at the western end marks the limit of a late advance of the ice during the Loch Lomond Stadial.

established Because the surface is so close to sea level and the loch is 310 metres deep, most of Loch Morar's bed lies far below the level of the sea a short walk away.

traditional Like Loch Ness, Loch Morar has its own monster, Mòrag. Reports of large unidentified creatures in the loch are occasional and unverified.

Why the sea lochs matter

established Shelter and deep water make the sea lochs valuable. Scotland's salmon farms are concentrated on the west coast and the islands, in sheltered sea lochs and sounds. In 2024 the industry produced 192,000 tonnes of Atlantic salmon, up 27 per cent on 2023, in areas the government survey groups as the North West, South West, Western Isles, Orkney and Shetland.

established The same geography shapes defence. The Royal Navy's Clyde submarine base at Faslane sits on the Gare Loch, a sea loch opening off the Firth of Clyde.

A mild coast: Inverewe

shared The same Atlantic water that floods the lochs keeps this coast mild for its latitude. At Poolewe, at the head of the sea loch Loch Ewe, lies Inverewe Garden. Osgood Mackenzie began it on a barren, exposed promontory. Wikipedia and most accounts date the start to 1862, while the Royal Botanic Garden Edinburgh's profile of the garden dates its first plantings to 1864. Historic Environment Scotland's listing reconciles the two: Mackenzie's mother bought the Inverewe and Kernsary estates for him in 1862, and the walled garden was complete and the first conifers planted by 1864.

established The garden lies at about 57.8 degrees north, further north than Moscow, yet it grows more than 2,500 exotic plants, including Wollemi pines, Himalayan blue poppies and Californian redwoods, and the National Trust for Scotland says a rhododendron is in flower there every day of the year. The Trust, the RBGE and other accounts credit the moderating influence of the Gulf Stream and the North Atlantic current, which keeps winters on this coast mild for the latitude.

established Warm water is only half the explanation. The RBGE notes that wind, not cold or rain, is the main constraint at Inverewe, with a recorded gust of 120 miles an hour in 1989. Mackenzie's first task was to plant a shelter belt of trees around the site, and it is that shelter, as much as the ocean, that lets tender plants survive.

established Mackenzie's daughter, Mairi Sawyer, developed the garden further and in 1952 gave it to the National Trust for Scotland with an endowment for its upkeep. The garden covers about 20 to 22 hectares within an estate of some 850 hectares.

Drowning again

established The coast's soft edges are changing fast. Much of the west is hard rock, but beaches, dunes and machair are not. The Dynamic Coast project, with researchers at the University of Glasgow, found in its second assessment in 2021 that erosion affected 46 per cent of Scotland's soft shorelines, up from 38 per cent four years earlier, at an average of 0.43 metres a year. Under a high-emissions future, 75 per cent of soft coasts are expected to be eroding by 2050.

established At least £20 billion of roads, railways and homes lie within 50 metres of Scotland's coast, and natural defences such as dunes protect some £14.5 billion of them. Without maintained defences and under high emissions, about £1.2 billion of assets could be at risk of erosion by 2050. Most of the at-risk assets are clustered in Argyll and Bute, Dumfries and Galloway, Highland and Orkney. Argyll and Bute and Highland between them hold most of the sea-loch coast.

shared The pattern is uneven. Parts of the Highlands are still rising slowly after the ice, while sea levels rise worldwide. Where the land rises fastest, the two effects partly cancel out. Where coasts are low and soft, as on the machair islands, the sea is gaining.

• "Sea loch" is the Scottish word for a fjord.
• Loch Fyne runs 65 kilometres inland from the Sound of Bute.
• Loch Morar is 310 metres deep but its surface is only 9 metres above the sea.
• The River Morar, linking the loch to the sea, is only a few hundred metres long.
• Scotland's coastline length depends on the ruler: the official estimate is 18,743 kilometres.
• Scotland has around 900 offshore islands, but only about a hundred have anyone living on them: 101 islands had residents at the 2022 census.
• Inverewe Garden, on Loch Ewe, lies further north than Moscow, yet a rhododendron is in flower there every day of the year.
• Most of Scotland's salmon is farmed in sheltered western sea lochs and island sounds.

• Disputed: how long Scotland's coastline is. The official estimate is 18,743 kilometres along the high-water line, but every published figure is an estimate. The length of a crinkled coast depends on the scale of measurement, and other references give figures as low as 11,800 kilometres.
• Myth: Loch Morar formed about 10,000 years ago. That is roughly when the ice left. The basin was deepened over many glaciations.
• Myth: Loch Morar is a sea loch. It was carved in the same way, but it is fresh water, cut off from the sea by a rock sill that was lifted above sea level as the land rose after the ice.
• Myth: Loch Morar is the deepest water around Scotland. At 310 metres it is the deepest body of fresh water in the British Isles, but a depth of 324 metres was recorded in the Inner Sound, between Raasay and the mainland, in 1943.
• Disputed: the monster Mòrag. Reports of large unidentified creatures in the loch are occasional and unverified.
• Myth: Sea-level rise affects all of Scotland's coast equally. Parts of the Highlands are still rising after the ice, which partly offsets rising seas. Erosion is worst on low, soft coasts such as the machair islands.
• Myth: Inverewe's exotic plants survive because of the Gulf Stream alone. The North Atlantic current keeps winters mild, but wind is the main constraint, and the shelter belt of trees that Osgood Mackenzie planted first matters as much as the ocean.
• Disputed: when Inverewe Garden was begun. Most accounts give 1862, the year the estate was bought for Osgood Mackenzie. The Royal Botanic Garden Edinburgh dates the first plantings to 1864, and Historic Environment Scotland records the walled garden as complete by then.