Thirty years ago, a Nenagh local called Paddy Mackey, who spent his younger years on Lough Derg at a time when the word “pollution” was rarely spoken, was cruising along the lake near Dromineer when he saw something shocking: the water had turned completely green. Algae, feeding off excess nutrients from farms, industry and households, was choking the lake. Two dogs died after drinking the water. The pristine lake of his childhood, so clean he’d drink its waters, had become a killer.
Armed with an official 1993 report declaring Lough Derg (the one bordering counties Clare, Galway and Tipperary rather than the one in Donegal) saturated with nutrient pollution, Mackey and a group of like-minded locals founded SOLD – Save Our Lough Derg. They held public meetings, plastered car back windows with SOLD stickers and lobbied tirelessly for the lake’s restoration.
Poor old Lough Derg. This once magnificent, pristine lake has been made filthy by our pollution. As the last major lake on the Shannon’s long descent into the sea, Derg carries the weight of everything that has flowed into the river upstream. It is, as scientist Dr Cilian Roden puts it, “the waste-paper basket of Ireland”. At a public meeting in Nenagh last year on the lake’s future, Dr Roden voiced wry concern about the €10 billion project to pipe water downstream of Lough Derg to the capital. “I know some people here are a bit concerned about the plan to send water from Lough Derg to Dublin,” he said. “I’m afraid, at times: does Dublin know what it’s trying to import?”
Treat Lough Derg like a bin, and it will show you what that looks like. In September, locals posted pictures on social media showing a neon-green lake resembling thick pea soup. Fed by excessive phosphorus and nitrogen and encouraged by our warming climate, cyanobacteria (also known as blue-green algae) multiplied explosively, forming thick carpets of green scum. Potent toxins released by the algae can kill dogs and livestock, sicken people with nausea and skin irritations, and make the water unsafe to touch or drink. Official reports point to the chief culprits: nutrient pollution from agriculture is the main one, followed by changes from man-made weirs, channelling, hydropower regulation and treating the lake as a storage reservoir for flood defences and recreational boating.
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Lough Derg is the lake that turns green – a visual sign of ecological distress, a system veering towards collapse. In this weakened state, the lake has become hopelessly vulnerable to invasive species such as the zebra mussel, first recorded in 1994. More recently, the quagga mussel – a native of Ukraine – has set up home in Derg’s waters. These mussels quietly established themselves for years without anyone realising it, only to be discovered almost by accident in 2021 by UCD scientist Dr Jan Robert Baar. By then, this aggressive invader was everywhere – a clear illustration of how quickly an invasive species can take advantage of a lake whose natural ecological defences have been repeatedly undermined by pollution.
Both zebra and quagga mussels have transformed Lough Derg in far from benign ways. Like underwater vacuum cleaners, they filter vast quantities of algae and plankton, making the water appear deceptively clean and clear. Beneath that veneer, their impact is insidious: the mussels disrupt the food chain for native fish and invertebrates, strip out the oxygen, and exacerbate the effects of algal blooms. In Lough Derg today, quagga mussels grow in staggering densities – up to 25,000 per square metre – smothering native species and clogging water intake pipes. If it’s drinking water we want, it’ll put a huge drain on public finances. In America, over five years, zebra mussels cost the water treatment and electricity generation industries $267 million.
Today, the lake is under siege from invasives, and the Government has yet to adequately resource the extensive scientific effort needed to monitor and combat them – at a basic level, to ensure they’re found as early as possible. The most effective – and by far the cheapest – defence against these invaders is to tackle the root cause, pollution, and restore the lake to its former good health, strengthening its ability to function correctly.
But restore it to what? What, exactly, is the real Lough Derg? It’s like staring at a face distorted by botched plastic surgery and trying to imagine the real person beneath. Lough Derg has been so reshaped by pollution that its original character is almost impossible to discern.
But the lake has left some lingering clues. Research led by Dr Cilian Roden suggests that not too long ago, parts of Lough Derg were naturally nutrient-poor, calcium-rich marl waters, home to an array of specialised life. Among them were delicate underwater stoneworts – plant-like organisms that thrive in clean, low-nutrient waters and whose presence signals unpolluted, healthy water.
Nearly all these species have vanished. But Roden and his team discovered a few survivors at Clery’s point on the western shore. Taken together with other evidence, they conclude that the “simplest explanation” is that Lough Derg was a marl lake in good ecological condition, far from the “very severely damaged” state it faces today.
What does all of this matter? If Lough Derg is to be cleaned up and restored, it’s logical to first have a clear idea of what it once was – a baseline, if you like – to guide any efforts and set goals for bringing it back to health. If it is naturally a low-nutrient lake, then it should be assessed as such.
When it was active, SOLD galvanised locals and the authorities and pressed for action against pollution. Their efforts weren’t in vain: councils upgraded sewage plants, and the idea that locals could advocate for the lake became widely accepted. They even publicly took on powerful farm lobby groups. Most crucially, SOLD normalised the idea that locals could advocate for the lake.
Lough Derg is drifting towards the same fate as Lough Neagh, that once great lake now all but dead. Reversing the damage isn’t impossible, but it demands ambition – a plan on the scale of the Shannon–Dublin pipeline, though it would cost only a fraction as much. A tenth of that budget could buy what money can’t replace: clean water, and a living lake worth passing on.
[ Newton Emerson: An orange-green split is looming over Lough NeaghOpens in new window ]
