River Shannon at a crossroads: €10 billion water pipeline to Dublin or salmon restoration in Limerick?

WHICH is preferrable; the restoration of a world-famous fishery in Limerick or spending billions of taxpayers money diverting polluted water to the citizens of Dublin?
First, a little background. There is a 26-kilometre stretch of the River Shannon, from the Parteen Weir to Limerick city, which in the early 1920’s was a unique salmon fishery.
The estimated annual salmon run was between 350,000–500,000 fish. In 1927, 414,000lb of salmon were caught on the river. Salmon weighing 55 lb or more were regularly caught using local, hand-crafted Enright rods at Castleconnell.
Then came the Ardnacrusha hydro power station which was officially opened on July 22, 1929 by President WT Cosgrave. The impact on salmon, trout, eels, lamprey and coarse fish was immediate and catastrophic.
Today, 100 years later, a second shock is about to hit in the form of Uisce Eireann’s Water Supply Project Eastern and Midlands Region.

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This project intends taking 4 m3/s (cubic meters per second or 4,000 litres per second) of water from just above the Parteen Weir and piping it, 170km across the country, to a new reservoir at Peamount, County Dublin.
There are essentially two reasons why the river just north of Limerick city was a world-class fishery.
First, Atlantic salmon migrate from the sea to reach freshwater to spawn. At the Thomond Bridge area in Limerick city they encounter the tidal limit and pass into fully fresh, non‑tidal water.
The salmon paused in huge numbers in this area to rest and recover before setting-out to points upstream on the 360km river.
Second, the previous, full natural flow from the upper Shannon produced ideal conditions to create the perfect salmon habitat, particularly just above the Doonass Falls in Castleconnell; rich, diverse riverbanks, oxygen‑rich water, deep holding pools and shallow gravel beds gave rise to famous salmon pools.
The Shannon Scheme entailed diverting water from the river at a newly constructed Parteen Weir down a 13km long canal, called the headrace, to the turbines in Ardnacrusha Power Station.
The water then exited to a constructed tailrace, 5km in length, before joining up with the old River Shannon in the city centre.
Post 1929, the annual average flow of water down the river was 210 m³/s. Of this, 200 m³/s was diverted down the headrace to Ardnacrusha for power generation and the remainder, a “compensation flow” of 10 m³/s, was diverted down the old Shannon river.
As the water level in the old Shannon fell from 210 m³/s to 10 m³/s, the old river was too shallow for the fish to migrate upstream, the spawning beds became exposed to birds and frost.
However, the “lordly” salmon kept coming up the estuary but now, because they instinctively swim towards fast water, they went up the tailrace, not the old river, where they encountered, literally, a concrete wall at Ardnacrusha.
Equally, the salmon and smolts coming down the Shannon entered the headrace and found themselves either trapped or mangled by the four turbines at the power station. Confused and exhausted, the fish died in huge numbers in the polluted water on either side of the power station.
It took 30 years, until 1959, before the ESB introduced a fish lift at Ardnacrusha; an ineffective lift still in use today.
This lift enabled the fish in the tailrace to go upstream and allowed the fish in the headrace to swim downstream into the estuary.
Despite the establishment of the River Shannon Salmon Management Programme in 1990, the number of fish ascending the lift in Ardnacrusha has fallen from 12,000 in 1964 to a miniscule 123 in 2024 and fishermen on the old river are now all but non-existent.
The requirement to maintain a minimum compensation flow of 10 m³/s down the old River Shannon is a statutory requirement based on the Shannon Electricity Act 1925.
This means that Uisce Eireann’s proposal to abstract 4 m³/s at the Parteen, under normal circumstances, must come from the flow of water to Ardnacrusha not the old Shannon river. The water abstraction will reduce by an equal amount the flow of water to the power station which is a carbon-neutral form of electricity.
How much of the water abstraction will reach households, business and hospitals in the Dublin region?
The pipeline includes multiple offtake hubs along the route presumably intended to supply towns and communities in the Midlands. Hence the 4 m³/s is very likely to be a minimum not a maximum and there is no pending legislation specifying a maximum abstraction.
Of the water reaching Dublin, 33%, or 1.3 m³/s, will be lost through leaks before reaching homes and businesses. This is due to an archaic, damaged pipe system dating back to the Victorian era. In most Western European cities the leakage is typically in the 10–25% range. In addition, existing Dublin data centres will use approximately 17% of the abstracted water or 0.46 m³/s.
Subtracting the leakage and Data Centre usage, approximately 2.24 m³/s or just over half of the abstracted water would reach homes and businesses in Dublin.
This abstraction will facilitate the further growth and centralisation of industry and population in Dublin, an area already suffering from chronic traffic congestion and housing shortage.
Uisce Eireann’s projection is that the abstraction project will cost between €4.6 billion to €5.9 billion but the Department of Housing estimates a cost of €10 billion in a worst-case risk scenario.
Ironically, the water being abstracted is polluted with a cyanobacteria, a blue-green algae, which produces toxins that can cause liver, kidney and brain disease as Lough Derg, the source of the water in the Parteen basin, is deteriorating in a similar fashion to Lough Neagh, Northern Ireland.
The “conservation limit” is the number of spawning salmon required to sustain the population. This is the biological replacement threshold. A figure of under 50,000 is estimated for the lower Shannon.
Instead of the further exploitation of an unique habitat and treating the Shannon as a trade-off between power and water supply, this is an opportune time to expand the narrative and add a third variable to the equation, namely ecology, and the restoration of the old River Shannon to a living salmon river.

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Salmon restoration cannot happen without an adequate supply of water and modern fish guidance systems to divert the fish to the old river.
As an example, starting from the pre‑abstraction situation, increasing the old Shannon flow from the current 10 m³/s to 50 m³/s, backed-up by serious habitat restoration in tributaries and spawning grounds and favourable ocean conditions, the old River Shannon could plausibly start to move towards the conservation limit.
This would reduce Ardnacrusha’s average available flow by 44 m³/s which corresponds to about 100 GWh per year in energy or about 0.3% of Ireland’s annual electricity consumption. A small price to pay for repairing the sins of the past.
- Written by Dr Anthony Leddin of Castleconnell and former head of the Department of Economics at the University of Limerick