The ESB lock at Ardnacrusha

Update 2019: ESB tours of Ardnacrusha are available again this year. Public tours run from 1 July to 13 September 2019.

Update 2017: the ESB is offering free tours to school groups and to the public in 2017. Tours for the public are available from 26 June through 1 September 2017; go here to book.


One of the earliest acts of the newly-independent Irish Free State was to harness the power of the River Shannon to generate electricity. The fall of the Shannon is concentrated in its lower reaches: it drops only 12m in the 185km from Battlebridge to Killaloe, but a further 30m between there and Killaloe. That drop made the construction of the eighteenth-century Limerick Navigation difficult: it linked Limerick, at the head of the Shannon Estuary, to Killaloe, at the foot of Lough Derg, using two locks on the Park Canal, a river section to Plassey, a canal with six locks to Errina, another river section up through O’Briensbridge and a final canal section with three locks through Killaloe itself. When the hydroelectric power station at Ardnacrusha was opened in 1929, that navigation became disused, with a new route provided through a lock at the power station.

Just to give an idea of why this lock is interesting, here is a photo taken from the top of the upper chamber, looking down at a 60-foot barge and a cruiser in the bottom of the lower chamber.

A very long way down

A very long way down (2003)

And for British readers, here is a 59′ narrowboat in the bottom chamber.

A narrowboat in the lower chamber (2007)

A narrowboat in the lower chamber (2007)

The total drop in this lock is about 100 feet or 30 metres: 60 feet in the upper chamber and about 40 in the lower. It’s “about 40” because the water below the lock is tidal so its level varies; the drop in the upper chamber can change too, as the level of water in the headrace varies with the number of turbines running.

Ardnacrusha is the deepest lock in These Islands. The lock is actually quite small, which enhances the effect when you’re looking up from the bottom.

The  power station is supplied with water from a headrace canal: a new weir at Parteen Villa allows the first 10 cubic metres of water per second down the river’s original course through O’Briensbridge and Castleconnell, but sends the next 400 cumec down the headrace. Anything left over after that is sent down the original course.

The headrace is a large, deep canal, spanned by three bridges; it leads to the power station, where a “double lock” (on Irish waterways, a staircase pair counts as one lock) drops boats down to sea level via a short canal that soon merges with the power station’s tailrace. It rejoins the Shannon’s original course near Corbally. After a short period, the navigation leaves the main course of the river and passes through the Abbey River, from which there is access to the old canal harbour at the foot of the Park Canal.

This page concentrates on the lock at Ardnacrusha; it does not cover the headrace, the tailrace or the navigation through Limerick in any detail. Suffice it to say that there are four turbines at Ardnacrusha; each one adds one knot to the current, which can also be swelled by rainfall upstream and by an ebb tide: peak flows of 10.6 knots were recorded under  Mathew Bridge in Limerick. Anyone proposing to use this route should plan the journey, time  it properly and take local advice.

Above the power station

We skip the first several miles of the headrace canal and begin at Blackwater Bridge, the closest to the power station at Ardnacrusha.

The power station seen through Blackwater Bridge

The power station seen through Blackwater Bridge (2001)

The power station seen from Blackwater Bridge

The power station seen from Blackwater Bridge (2007)

You can see that there is a considerable flow as the turbines draw water into the power station.

The power station from just past the bridge (2001)

The power station from just past the bridge (2001)

The tall part on the left houses the guillotine gates for the upper chamber of the lock.

The lock is operated by the Electricity Supply Board (ESB). It has a wonderful machine for clearing blockages from the intakes to the turbines.

The wonderful machine 1

The wonderful machine 1 (2007)

The wonderful machine 2 (2007)

The wonderful machine 2 (2007)

There is a small waiting jetty above the lock.

The waiting jetty (2007)

The waiting jetty (2007)

Power station

Before we examine the locks, let’s have a quick look at the power station itself.

Looking down from the upper level

Looking down from the upper level (2001)

The tall building on the left houses the bottom gates; just in front of it is the lower chamber, which is full. To the right of that is the spillway through which the chambers are emptied into the same area as the outflow from the turbines. The turbine hall is the large building on the right, with its copper control room, which won an architectural award in 1996.

The control room

The control room (2007)

I understand (if I’ve got this wrong, please correct me) that nobody works on the generation side at Ardnacrusha any more; the turbines are switched on and off from the ESB pumped storage facility at Turlough Hill.

Here are the penstocks feeding the water from the headrace to the turbines. Ardnacrusha was originally designed to have six turbines but it was found that there was only enough water for four. Three were installed ab initio and a fourth in the 1930s.

The penstocks

The penstocks (2007)

I’m not sure how many turbines are operating to produce the outflow shown in this next photo, but I imagine only one or two.


Outflow (2003)

One of the unused penstock bays was later adapted to provide a large fish-pass, intended to let salmon get upstream through the power station. It is in effect a large vertical cylinder; fish swim up and pass out at the top through the dam into the headrace. If you have more details on its innards or workings, do please leave a Comment below. The cylinder is the part with the grey boxes on top; the fish then swim towards the viewer.

The fishpass

The fish-pass (2007)

You can explore the links between salmon, choirs, evolutionary algorithms and Ardnacrusha here. There are some photos of the turbine hall under Images.

Here is the space between the dam and the turbine hall, over the top of the penstocks. I’d love to know what that track is ….

The mysterious track (2007)

The mysterious track (2007)

Upper chamber

Here’s the top gate from the outside. A cruiser has just gone in and the gate is being closed.

The top gate from outside the lock

The top gate from outside the lock (2001)

The gate (2007)

The gate (2007)

The upper works (2007)

The upper works (2007)

The sides of this chamber are quite high, even when the lock is full, so boats usually pay their tolls in the lower chamber, where it’s easier to get on and off the boat. If you give some notice, and the  lock isn’t too busy, the keeper is usually happy to give you time to look around and take photographs.It is possible to get on or off by ladder in the upper chamber.

The high sides of the upper chamber (2007)

The high sides of the upper chamber (2007)

Here is the top gate, with its cill, while the chamber is being emptied.

Top gate and cill (2007)

Top gate and cill (2007)

While cables have been added in recent years, the traditional method of holding on is to use the hooks in the side walls. Note also the ladders (which I would hate to have to climb). As there are no gate racks (paddles), there is very little turbulence in the lock.

Hooks and a ladder

Hooks and a ladder (2007)

Hooks and a ladder from below (2001)

Hooks and a ladder from below (2001)

There are zebra mussels on the walls of the upper chamber but not in the lower, perhaps (as Mike Miller suggests in the Comments below) because it is kept empty.

Here are the upper gates rising.

Upper gate rising 1

Upper gate rising 1 (2007)

Upper gate rising 2 (2007)

Upper gate rising 2 (2007)

Finally, here are the two banks of the upper chamber. Note the large bollards, now no longer accessible, in both photos.

Land-side bank of upper chamber (2007)

Land-side bank of upper chamber (2007)

Turbine-side bank of upper chamber (2007)

Dam-side bank of upper chamber (2007)

Passing through the upper chamber

For some reason, I have more pics of boats coming up from Limerick than of those descending thereto. Here’s one, though.

Cruiser descending in the upper chamber (2001)

Cruiser descending in the upper chamber (2001)

Barge and cruiser entering upper chamber from lower (2003)

Barge and cruiser entering upper chamber from lower (2003)

The following photos show NB Earnest in 2007; you can get an Earnest-eye view here (going down) and here (back up).

NB Earnest rising in the upper chamber 1 (2007)

NB Earnest rising in the upper chamber 1 (2007)

NB Earnest rising in the upper chamber 2 (2007)

NB Earnest rising in the upper chamber 2 (2007)

NB Earnest rising in the upper chamber 3 (2007)

NB Earnest rising in the upper chamber 3 (2007)

NB Earnest rising in the upper chamber 4 (2007)

NB Earnest rising in the upper chamber 4 (2007)

NB Earnest rising in the upper chamber 5 (2007)

NB Earnest rising in the upper chamber 5 (2007)

Leaving the upper chamber heading upstream (2007)

NB Earnest leaving the upper chamber heading upstream (2007)

Meanwhile, going in the other direction ….

Passing from the upper to the lower chamber (2001)

Passing from the upper to the lower chamber 1 (2001)

Passing from the upper to the lower chamber 2 (2001)

Passing from the upper to the lower chamber 2 (2001)

The lower chamber

All my photos show boats rising, not descending, in the chamber. The first shows a barge and a cruiser in the lower chamber.

Barge and cruiser in lower lock (2003)

Barge and cruiser in lower lock (2003)

That photo was taken from the lower control room, which is shown in the next photo.

Lower control room

Lower control room (2007)

The next photo was taken from the deck of a sailing-boat in the lower chamber, looking up at the gate dividing it from the upper chamber.

Looking up from the lower chamber (2004)

Looking up from the lower chamber (2004)

The curved wall at the top of that photo is what is holding back the contents of the upper chamber. You can see the lockkeeper near the top and a bar across the lock below him.

The wall of the upper chamber (2007)

The wall of the upper chamber (2007)

Here’s the same bar, seen from above (from the lockkeeper’s platform) with the bow of the barge below it.

Barge bow (2003)

Barge bow (2003)

And here are some views of NB Earnest rising in the lower chamber (all in July 2007).

NB Earnest rising in the lower chamber 1 (2007)

Note the small bollard

NB Earnest rising in the lower chamber 2 (2007)

Note the old and new (large and small) bollards as well as the safety fencing installed some years ago

NB Earnest using the wall hooks. Note the spillway on the right

NB Earnest using the wall hooks. Note the spillway on the right

Openings to spillway (2003)

Openings to spillway. I’m not clear on how the system works, though (2003)

The middle gate has lifted and the boat enters the upper chamber

The middle gate has lifted and the boat enters the upper chamber

Below the lock

The short canal below the lock is itself usually fairly calm, but it soon joins the tailrace, where the current reflects the number of turbines in operation. And more turbines may be turned on at any time while you’re in the stretch between Ardnacrusha and Limerick; no account will be taken of the presence of any boat in the navigation.

This photo shows the short canal and, coming in on the right, the tailrace; they meet just behind the clump of trees in the middle.

The short canal and the tailrace

The short canal and the tailrace (2007)

Here’s a view under the bottom gate and down the canal. Some pontoons have since been installed as a waiting jetty; before then, you had to hang on to chains along the sloping wall on the right.

Looking under the gate down the canal

Looking under the gate down the canal (2001)

The next photo shows the old chains; the barge is moored to the new pontoon.

Chains and pontoon

Chains and pontoon (2003)

I know that the architecture isn’t really as enchanting as that of the castles of the Loire, say, or even of Lismore, but Ardnacrusha in the distance is still pretty impressive. The next photo, taken from Parteen Bridge, also gives an idea of the current in the tailrace …

Battling upstream to the enchanted, er, power station (2007)

Battling upstream to the enchanted, er, power station (2007)

… as does this one.

Full steam ahead (2007)

Full steam ahead (2007)

Finally, this next photo, taken from a boat that has just left going downstream, shows all the levels of the lock.

The lock from below

The lock from below (2001)

Operation and equipment

Unlike the other locks on the Shannon, which are controlled by Waterways Ireland, this one is operated by the ESB (Electricity Supply Board), which has spent a considerable amount of money on maintenance, upgrading and improved safety in recent years.

Update February 2012

The gates are now interlocked, which means that the upper chamber can not be filled until the lower has been emptied. As a result, the cycle time is now about 90 minutes: in other words, if there are more boats than will fit in a single locking, some of them will have to wait for 90 minutes to be admitted to the chamber.

The chamber is 105′ X 20′ (slightly narrower in one place). It can accommodate a Grand Canal size barge and a cruiser, or two 36′ cruisers at a time.

The water level in the headrace varies with the number of turbines running; in consequence, the headroom (air draught) under the top gates can vary from 12′ to 16′. The middle gate has 13′ 2″ of headroom and the bottom gate headroom ranges from 11′ to 20′, depending on the state of the tide.

The lock should be booked at least two days in advance. No toll is now charged. The lock passage itself takes about an hour and uses (someone once told me) about a million gallons of water.

Let us finish with a few photos of aspects of the operation of the lock. The first set shows the old control system, which was replaced during the winter of 2008/9; these photos show machinery that no longer exists.

The upper chamber is controlled from this room between the two chambers (2007)

The upper chamber is controlled from this room between the two chambers (2007)

Old equipment 1 (2007)

Old equipment 1 (2007)

The lower chamber is controlled from a similar room over the bottom gates. For some reason, this had black equipment.

Old equipment 2 (2007)

Old equipment 2 (2007)

There were clear instructions for the lockkeeper.

Old equipment 3 (2007)

Old equipment 3 (2007)

Then there are the spillways.

Spillways 1 (2007)

Spillways 1 (2007)

Spillways 2 (2007)

Spillways 2 (2007)

Spillways 3 (2007)

Spillways 3 (2007)

Spillways 4 (2007)

Spillways 4 (2007)

Spillways 5 (2007)

Spillways 5 (2007)

Finally, there is provision for stop planks below the lower chamber, with an overhead railway to carry them into position.

Stop planks 1 (2007)

Stop planks 1 (2007)

Stop planks 2 (2007)

Stop planks 2 (2007)

Stop planks 3 (2007)

Stop planks 3 (2007)

As usual, if you can correct, clarify or amplify anything on this page, do please leave a Comment below.

Visiting Ardnacrusha

The ESB offered tours in 2017 and 2018; here is the information for 2018.

More info

Some more photos of Ardnacrusha here. Some photos, from the 1920s and 1930, of Parteen Villa Weir here and an account by Siemens here with an interesting list of the plant used in construction, including 31 barges, tugs, launches and pontoons. Clare County Library has much material, including here and here. The ESB archives site has the 39 reports made by Siemens during construction here.

Here is a kayaker‘s account of a passage through Ardnacrusha and here are photos of the IARU expedition along the headrace and through Ardnacrusha lock in May 2011 (click on a photo to see a larger version).

If you have some time to spare, you might like my slide show of a trip on a barge from Killaloe through Ardnacrusha to Limerick. It has about 300 photos, taken from the barge, so you get to see what the whole trip is like. You can let the slide show run by itself or click through faster if you prefer. All 300 photos have to be loaded on the page before the slide show starts running, so don’t panic if it takes a while to get ready.

If you would like to be kept informed of updates to this site, subscribe to the RSS feed on the front page.  That way, you’ll get a brief notification of any updates or additions, and can decide for yourself whether you want to go and look at them.

Here is a page about the bleach mill at Doonass and here is another about the bleach mill at Clareville: they both made use of the Shannon’s horsepower before Ardnacrusha was built.


48 responses to “The ESB lock at Ardnacrusha

  1. Excellent information – makes me think of coming but I have 3.9m beam… and I think I might have a few problems…

  2. You should get through the Grand Canal with 3.9m (which I think is 13′, slightly less than the Grand Canal Company motor-barges) and beam would be no problem on the Shannon. Draught on the Grand Canal might be difficult, though! See Hawthorn’s blog at


  3. I think that Zebra mussels only in upper chamber is because normally the upper chamber is left full while the lower chamber is left empty.

    David Killeen’s dad built the fish pass.

  4. You may well be right. I’ve emailed the oracle to ask for his view!


  5. Follow-up about the mussels: Dan Minchin of the Lough Derg Science Group (see Non-WI workboats page) points out that there are zebra mussels in the tailrace and down to Limerick docks, so they can live in the tidal water. I’ve amended my text above.

  6. Hi
    A very good pictorial and edited presentation.
    Makes me more determined than ever to do the trip .
    Must ask Pat Lysaght to do it for myself and a few friends during the summer.
    Well done.
    Pat Sheehan

  7. Thanks again, Pat.

    There is a photo of Pat Lysaght on my workboats page about halfway down. It’s a long page so takes a while to upload.

    I think, for a first visit, “uphill” through Ardnacrusha is even better than “downhill”. The power station seen from water level is awe-inspiring. bjg

  8. Hi
    -I will be in the area of Ardnacrusha early June this year during a tour by car, can anyone advise re.non boater access to the area of the lock etc?
    -ie car parking, extent of visitor access and so on.
    Thankyou Simon M (NB Callipygian,Staffs and Worcs Canal,Wolverhamton,England)

  9. Access to Ardnacrusha is limited: in general, the ESB admits only (non-commercial) groups, which are booked in advance; tours can be provided only at set times on Mondays through Fridays. I have sent some further information directly to Simon about this. bjg

  10. Hi
    I will be in around the Portumna area from 31st July for a week, as a non boater are there any companies that take day trips to Ardnascrusha? With no boating experience I would rather not have to hire a boat myself.
    Regards, Helen

  11. Helen
    To the best of my knowledge the only firm that is licensed to carry passengers through Ardnacrusha is Spirit of Lough Derg, but you may have to book for a group of twelve. It’s run by a very nice chap, so it might be worth emailing him to see if he has a trip with less than twelve going through while you’re in Portumna.
    The cruiser-hire firms will not allow you to take a boat downstream of Killaloe, so you can’t get to Ardnacrusha that way.

  12. Gerard Condon

    Hi guys I have alot of original black and white photos of the contruction of Ardnacrusha, from the turning of the first sod to near completion. Would you know of any body who may be interested in these Photos.
    regard Gerry C

  13. I have replied directly to Gerry about this. bjg

  14. Frank Schillinger

    Hallo, my Name is Frank and from the Black Forrest.
    I m very interessting for the picture. Please send me some Picture via E-Mail. I´m very happy about this.
    Thank you very much

  15. Hello,
    I visited the Hunt Museum last year and saw an exhibition of photos taken during the construction of Ardna Crusha. (Photographer was Franz Sebastian Haselbeck 1885-1973). It also included paintings by Sean Keating.
    I too would be very interested to visit the power station, by land if not by boat. Could you pass me the details of who to contact, in order to arrange this?
    Thank you,

  16. I’ll email you direct, but I think that ESB admits only groups. bjg

  17. That is a magnificent article on a splendid bit of engineering. We’re due to visit the area around Easter this year, do you know if it’s possible to gain access to take some photos of the locks in particular or is it all out of bounds.

  18. Thanks, Paul. I’ll email you direct about access. bjg

  19. Hi Brian,

    I have created a short video of a recent transition through the lock that you may want to link to on your website.


  20. I think the link works OK; thanks. bjg

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  26. wow great! Really interesting read and great pics thanks

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  28. very interesting indeed.what percentage of power does it supply to the national grid and how does it compare as far as cost per unit of electricty is concerned to other producers

  29. The answer to the first question is 2%. See this page for info on all ESB stations. I have no idea about costs; I suspect they are low as the station is unstaffed and the fuel is free, although there are still maintenance and other matters to deal with. bjg

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  31. Hello,

    I see there is an open day Sunday 11th from 11 to 2. We are living across the road from the station but tried to gain entry last October but it was full . Can we prebook a slot for Sunday .

    Kind regards,

    Suzanne & paul butler

  32. I’m afraid I have nothing to do with the ESB. I see here that booking was possible, indeed essential, as the event is now booked out. bjg

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  35. A little knowledge is a dangerous thing! That’s me, having walked the Lough Derg Way from Limerick to Killaloe recently, and gone up through the locks at Ardnacrusha on a Guinness barge in the 1950s. During, or before, the Nov/Dec 2015 flood crisis, if significantly more water was left down the Headrace from Parteen Dam, could that increased amount be left through at the power station, especially during low tide?

  36. It’s an interesting question, and would probably need an engineer to give a proper answer. I did wonder whether water might be let through the lock (on the assumption that the penstocks and turbines couldn’t take more than they get) but there is a danger that excessive flow could damage the works.

    On the other hand [and here’s even less knowledge being displayed] someone told me that each lock cycle takes about an hour and uses 1 million gallons of water. I’ve just converted 1 million gallons per hour to cubic metres per second; if this online conversion site is correct, the answer is 1.262 802 777 8 cumec, just over one and a quarter. Which, compared with the 400 going through thr turbines, is not very much. Even if you got the water through in fifteen minutes, you’re only up to 5 cumec. But maybe someone more knowledgeable can correct me …. bjg

  37. Geoff Woolley 'Snow Mouse', Belturbet.

    Thank you for a great description, photo’s etc. and the time you gave up to post it. We passed through in 2016 en route to the Med and found the ESB staff very pleasant and helpful. Pat Lysaght’s guidance down the tailrace through to Custom House key is invaluable.

  38. Thank you. bjg

  39. You asked to leave a comment on the said fish pass at Ardnacrusha, I would like to point out that this salmon pass is a ONE way system and any salmon that go through this pass is on a one way ticket there is no way back for them, sadly it has taken its toll on the famous Shannon Salmon, it is no longer a common sight on the upper regions of the river Shannon, lost forever unless the ESB do something to save them by installing a proper fish pass that salmon has FREE PASSAGE through the ESB Hydro Station and the DAM at the other end of the head race known as Parteen Weir.
    Very sad to see this slow death of the salmon on the river Shannon .

  40. Sorcha O'Brien

    Gerard Condon: It’s probably an incredibly late reply given that you posted in 2011, but the ESB Archive would probably be really interested in your photos of the construction, as would I (I don’t work for them, but am writing a book on the images of the station under construction). Their new website is The Siemens engineers took a huge number of photos during the construction – I wonder if they are the same photos?

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  42. Hello there.. I was hoping to visit before September.. just wondering would my daughter be able to come with us, our daughter is a wheelchair user… is the tour wheelchair friendly?? If not will have to sort out a babysitter.. please help Mary..

  43. I don’t know, I’m afraid: you would have to ask ESB. The site includes a drop of 100 feet (from the level of the river above to that below the power station). My recollection is that there may be steps in some places, but ESB is pretty good about equality of access so I’d ask them direct. bjg

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  46. The “mysterious track” looks a lot like a giant cable tray. My guess is that at some point they needed to replace the wiring from the generation hall out to the switch yards, and opted to build a new external one. So I’d imagine there are just a giant bunch of electrical cables in there.

  47. Thank you. Good to have a knowledgeable contributor! bjg

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