Pollution on the Liffey: Algal blooms at Blessington a threat to Dublin’s drinking water

The Blessington Lakes, as they are known locally in this part of Co Wicklow, have been a shape-shifting place for decades. A century ago, this enormous body of water, some 26 square kilometres in size, did not exist. It was all rural fields and villages.

Between 1937 and 1940, Poulaphouca Reservoir, as it is officially known, was created when the river Liffey was dammed in a joint project by Dublin City Council and the ESB to supply water to Dublin and environs. People were relocated elsewhere, and the villages they had lived in, and the fields where they walked, were submerged.

The reservoir was named after the local waterfall that no longer existed once the dam was created. The Irish name references the “púca” or “pooka” – a ghost or fairy. The placename translates as the “Ghost’s Hole”, which seems a pertinently haunting reminder of those people who once lived in the place where much of Dublin’s drinking water now comes from. The Liffey enters at the north of the reservoir, at Threecastles.

There is a prominent sign by the water’s edge, placed there by the ESB. It says: “Warning of algal bloom. At times, this area of water may be affected by algal blooms or scum, causing a discolouration of the water. Illnesses including skin rashes, vomiting and diarrhoea may result from contact with the affected water. Algal blooms and its related scums can be highly toxic to dogs and other animals.”

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Elaine McGoff, head of advocacy at An Taisce, walks by the water. There are a number of boats pulled up on the grass: Lady Frances, Wild Rose, Pike Hunter, Josie B, Molly. All of them require permits from the ESB to go out on the water. Sailing and kayaking also take place here, but swimming is not allowed.

“Here,” she says, pointing to an area where the water meets the shore. “A few days ago, this was where I saw the algal bloom.”

McGoff stretches out an arm to indicate the breath of the bloom. It’s a metre wide. Today, it’s gone, although she says she received word from a friend that it was seen the previous day at Valleymount, at another point on the reservoir. She takes out her phone to show pictures of an almost-fluorescent green bloom.

The algal bloom is not a new phenomenon at Poulaphouca.

“We’ve seen it previously in August and September,” McGoff says. “What’s new is seeing it this late in the year, in October. It’s partly the impact of climate change, because it is a fact the water is getting warmer. But it’s also a fact that more pollution is getting into the water. Slurry, waste from septic tanks, run-off from forestry, livestock. The bloom is bright green and it is a bacteria. There is a fear that the spores might be airborne.”

McGoff references the catastrophe at Lough Neagh, where an algal bloom is the most virulent it has been since the 1970s. The impact on the vast Northern Irish lake – at 400 sq km the largest on the island – is on fish, bird and insect wildlife. The bloom is so prevalent it is actually a thick slick atop the water. People have been warned not to let their dogs enter the lough.

Tommy Deegan, who lives in Ballymore Eustace, Co Kildare, a short distance down the Liffey from Blessington, established the angling club in the town in 1974.

“We started the angling club because the water quality was so badly polluted back in the 1970s,” he says.

They had 400 people join up. Today, there are some 160 active members.

Deegan says that in the 1970s the Liffey in Ballymore Eustace was “a chocolate brown colour”. (Dubliners may recall that in the 1980s the Liffey in central Dublin was referred to as the “Sniffy Liffey”, such was the bad smell it regularly emanated.)

“We saw that the fish coming out of the river were stunted in growth,” he says.

They fished for salmon and trout in those days; it is now forbidden to fish for salmon, as the stocks are so depleted, but trout fishing continues.

[ Algal bloom strikes at second large drinking-water reservoir in Co Wicklow ]

An estimated 50 per cent of all the drinking water for Dublin comes from the Poulaphouca reservoir, the biggest in Ireland. The water is treated at the Ballymore Eustace water treatment plant, the largest in the country.

Deegan has an extraordinary knowledge of the intricacies and chemicals required to treat water, mentioning “aluminium sulphate”, “floc” and “polyelectrolyte” – some of the science behind the process. Deegan’s key point is, as he says: “Water treatment is a dirty industry.” Add to all that the emergence of the algal bloom in the place from which Dublin receives so much of its water, and the future challenges become even more complex.

“I’ve seen algal at Golden Falls too,” Deegan says, referring to the hydroelectric power station on the Liffey in Co Kildare, which is not far from the home of the Golden Falls Waterski Club.

Deegan has health concerns for his angling colleagues who go out to fish trout on the Poulaphouca Reservoir, which are restocked annually by the ESB.

“Some take their trout home and cook them. Are they safe to eat? Nobody has told us. Nobody has been sick yet, but we don’t know the impact in the future if the bloom gets worse,” he says.

Deegan’s son Steve Deegan, who also lives locally, is chair of Ballymore Eustace Community Development Association. Looking out over the surface of the reservoir, he notes that there are “holy wells under there too”.

Deegan points to some locations that, in addition to Poulaphouca, have become amenities for the area, all connected with the water. There’s the 5.5km Blessington Greenway, which links Blessington to Russborough House. The water is in view from much of the greenway. There’s the Golden Falls reservoir, with the ramp for its waterski club, which is licensed to them by the ESB.

“A waterskiing competition here had to be cancelled last year due to bloom,” he says.

The algal bloom makes for startling images, due to its high visibility and arsenic-green hue. Images of a green slick on the water is also an easier way to understand the impact of the pollution around here and points to the huge challenge in ensuring that a reservoir which provides so much of the drinking water for Dublin’s population – sourced ultimately from the Liffey, which fills the lakes – remains protected and pollution-free.

“We want to make sure Poulaphouca survives as an amenity and doesn’t become a sewer,” Deegan says.

On Tuesday: Kevin O’Sullivan examines how the Dublin area is over-reliant on the vulnerable Liffey for its drinking water supplies