The Mysterious Dry Lakes of Ireland


A turlough, or turlach, is a mysterious disappearing lake, found only in Ireland. (Well, there’s just one in Wales.)


A turlough, or turlach is a fascinating feature of our landscape. And, much like the Irish, it disappears in the summer, only to reappear when the weather turns bleak. Yes indeed, it is uniquely Irish.

Mostly, these lakes appear and disappear in the same locations in Ireland. They found mostly in limestone areas, west of the River Shannon. The name comes from the Irish “tuar”, meaning dry, with the suffix “lach”, meaning a place (in an abstract sense). The “lach” suffix is often mistakenly thought to refer to the word “loch”, the Scottish Gaelic and Scots word for lake. But that isn’t the case. Roughly translated, it means a dry lake that could appear anywhere.

The reason why turloughs are so mysterious is that they are bodies of water that just “appear” in low-lying areas, but don’t have an above-ground river or stream that feeds into them. In fact, they burst forth via springs wherever they damn well please. And they can disappear just as fast, leaving you wondering why your sheep were previously drowning and now they are not, and your shoes are wet. In fact, your jeans are wet as well. And possibly your hair.

To the east of the Shannon, limestone has capped the earth, thus the rainwater does not sink into the soil as usual. In fact, there is no proper surface river network. Instead, the rainfall flows through openings in the rock and flows into deep underground systems. In times of lighter rainfall, the rainwater’s journey underground is a jolly one to the sea. However in times of insane rainfall, the underground routes become overburdened: water running underground breaks its “banks” and busts out onto the surface of the earth from underground. And this gushing spring creates a turlough – a lake that appears, and then disappears when the water roads under the land become less congested and can suck the water back in.

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This picture of a turlough was taken by Geomorphologist Mary Bourke.  Follow her on Twitter here.

Spring water is seen as the most pure and healthy water around; Irish people have had a very special relationship with spring waters since the beginning of time. So if a spring appears in your front garden, you could consider yourself lucky. You don’t have to buy Ishka Natural Spring Water anymore – famous for running through limestone in Limerick. Your own personal spring could be running through your rosebeds. However if your personal spring develops into a turlough you might want to grab your cat and run.

As we all know well in the last few years, the rains falls a lot in Ireland. An interesting thing to note is that while turloughs have appeared and disappeared in pretty much the same places for centuries in Ireland, there appears to be several new turloughs appearing where there weren’t any recorded before, due to the insane and largely unfair amount of rainfall over the past few years.

According to Foss Environmental Consulting, new turloughs have been found all over the gaff in County Monaghan. Four of the newly discovered turloughs were deemed to be of International importance and two of National importance due to their size, quality and geographic location. “These sites represent a significant biodiversity asset for county Monaghan and should be afforded the highest level of protection.”

Depending on rainfall, turloughs can appear almost instantly. An appreciable amount of water can collect in one hour, and disappear in an equally short time. Some turloughs hold permanent water on their floors, while others show no water at all when rainfall is absent. Sometimes, the water disappear once again through the porous floor of the turlough, in other turloughs, the water disappears through a swallow hole. Swallow holes, locally known as “slugga”, or a “swallet” can be seen once the lake as drained.

A swallow hole.


Most Turloughs have an inflow spring at one end, and a swallow hole somewhere else in the ground where water drains away. But some turloughs fill and empty through the same hole. The water sinking in the swallow hole travels underground and can re-emerge kilometres away at yet another spring or turlough.

Most turloughs flood to a depth of about 2 metres (6.6 ft) but some are much deeper: for example, some of the turloughs near Gort reach about 5 metres (16 ft) deep in midwinter. The largest turlough in Ireland, Rahasane turlough, which lies to the west of Craughwell in County Galway, covers about 2.5 square kilometres.


Rahasane turlough

Rahasane turlough has no surface outlet and is surrounded on all sides by rising land. It is the largest surviving turlough in Ireland. Water collects seasonally in the basin and drains away only through evaporation or seepage into the underlying limestone. It consists of two basins which are connected at times of flood but separated as the waters decline. In the summer the lake empties and the basin is grazed by cattle, horses and sheep. The southern basin is the more impressive feature, with high rocky sides above an undulating base, strewn with boulders. Like many other large turloughs it has been threatened with permanent drainage for agricultural improvement, however, it has now been designated a Special Protection Area. It is an important location for migrating birds, and wintering ground for the White-fronted Goose. It is one of the few known breeding grounds in Ireland of the Eurasian Wigeon. The fairy shrimp Tanymastix stagnalis was first recorded in Ireland from the southern basin at Rahasane. It cannot occur in permanent waterbodies as it needs isolation from predators in order to grow to reproductive age.

Eoou, What is That?

Limestone is made from the mineral calcium carbonate. As water washes by it, it picks up some of the calcium carbonate for a ride.  This is what makes hard water and causes furring on the inside of kettles, as the calcium carbonate comes out of solution when the water is heated. Something similar happens in turloughs – water that has picked up a lot of calcium carbonate during its underground travel rises in the turloughs. Some of the calcium carbonate comes out of solution and forms a white deposit. If a turlough has emptied recently, a whitish coating on the vegetation on the turlough floor may be visible. This is great for livestock, as animals need calcium carbonate to form their skeletons. In addition, algae grow while the turlough is full, and its smelly corpse is left behind as the waters drain away. This is excellent for the soil.

However, farmers have had love-hate relationships with turloughs for a long time. Turloughs provide good summer grazing for cattle, sheep and horses, partly because of the annual deposition of lime-rich silt. But, of course, many farmers would like to use the land for grazing, and would like to be able to predict when they turloughs appear, or don’t appear. Many farmers have created draining channels to divert the water away and into streams. At least a third of the turloughs in Ireland have already been drained and more are being drained each year. This has very serious consequences from the point of view of the environmentalist – the unique flora and fauna of the turlough cannot survive in the absence of seasonal flooding. Even for the farmer, the benefits of draining the turlough are not always win-win. Halting the annual limey silt deposition means that the soil may become impoverished and fertilisers must be used. So while turloughs are an interesting and a vital part of the Irish environment, for farmers they can be an annoyance. It all depends on the farmer, and the turlough.

A turlough is a fascinating part of the Irish landscape. And the best part of it is that it is uniquely Irish (nearly). So off you go to find your nearest local turlough. And email us with pictures when you do.



As a Name

As an interesting side-note, “Turlough” has been used as a boy’s name over the centuries, although the name has gone in and out of fashion over the decades. Turlough, or the alternate spelling, “Turlach” is usually translated as Terence and Terry, two names that have become strongly associated with Ireland. Turlough O’Carolan was a 17th century blind harpist and composer who wrote one of the most haunting pieces of Irish music, O’Carolan’s Concerto. In old Irish, is it spelt Toirdhealbhach, pronounced more or less “TORE-lukh.” Note the importance of the guttural “kh” sound. Turlough, an Anglicisation, is pronounced as “TUR-low.” Toirdhealbhach is used chiefly in the Gaelic and Irish languages, and its origin is Celtic. In modern times, Vislor Turlough, known as “Turlough”, is a fictional character played by Mark Strickson in the long-running British science fiction television series Doctor Who. He was a companion of the Fifth Doctor, being a regular in the programme from 1983 to 1984.

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