One summer’s day a few years ago, I walked along the waterside vegetation on the edge of Lough Carra in Mayo, searching for a slim-bodied insect just 32mm long, which tended to dash and dart through the air with phenomenal speed. Fortunately, given that the insect in question was brilliant blue, reasonably common and in occasional need of a break, it didn’t take long to spot it clinging to a seed head with its slender legs.
What I was looking at – the exquisite black-and-white striped common blue damselfly – has barely changed in 300 million years.
Lough Carra is a place of immense uniqueness. With an average depth of just 6ft, it lies on a bed of limestone formed hundreds of millions of years ago, and its waters are saturated with calcium carbonate. A white layer of “marl crust”, which develops over time like tartar on teeth, covers the rocks on the lakeshore. Inside live billion-year-old cyanobacteria and silica-covered diatoms.
That day on Lough Carra came to mind while reading a new, freely available book, The Lakes of Ireland – Mirrors of Change, which lays out across 22 chapters what has been gleaned from decades of research on Ireland’s 14,000 lakes and ponds. The authors, water scientists and researchers, share what they know and, most crucially (because you can guess where the trends are going), offer suggestions about what can be done to keep our lakes natural.
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Judging whether a lake is in good health can be tricky, but contributors Cillian Roden and Aine O’Connor offer a simple metric we can all use: water clarity. Gin-clear water allows the sun to penetrate through the waterbody, fuelling the growth of submerged plants, which in turn release oxygen.
Take Ballynakill Lough in northeast Galway, which is, according to Roden and O’Connor, one of our most exceptional lakes. “It’s doubtful if a comparable lake survives in western Europe,” they write. Ballynakill is home to species otherwise absent across much of Europe, such as pipewort and water lobelia, along with an abundance of the minuscule, whorled “least stonewort”, aquatic algae.
In 2004, a rare aquatic plant known only in one other lake, nearby Rusheenduff Lough, was discovered, along with the ribbon-like, light green slender naiad, which provides refuge for fish and invertebrates, food for rare ducks and, most crucially, releases plenty of oxygen.
Lough Cooloorta’s turquoise-blue colour in nearby Clare is reminiscent of water over coral reefs. This crystal-clear lake allows sunlight to reach up to 10m below the surface, and a plethora of species are found. These include 12 different stoneworts, which play a central role in keeping the water pure by absorbing excess nutrients, and flowering plants such as the soft-water bulbous rush, which thrives in low-nutrient lakes.
The marl crust in Cooloorta, which is orange-brown, is home to one of the rarest water beetles in Europe, Ochthebius nilssoni, known in Irish as Ciaróginbán. Found in 2019 in Lough Carra, this beetle is only known in one locality in Sweden and another in Italy.
Ballynakill and Cooloorta are outliers. Of our 14,000 lakes and ponds, only 224 are monitored by the Environmental Protection Agency. And while 69 per cent of those assessed are in high or good ecological status, lake water quality has not improved in 50 years. The pressures of nutrients from agriculture, bogland degradation and excessive drinking water abstraction have rapidly taken their toll.
Co Kerry’s Lough Leane, which was once of European importance but is now loaded with nutrients, is “quickly approaching the state of Lough Neagh”, write Roden and O’Connor. “Clearly, lake habitats in Ireland are quickly degrading, and just as we lost our great forests in the seventeenth century and our equally wonderful raised bogs in the twentieth, we must expect to lose our extensive lake ecosystems in the twenty-first century unless we rapidly reduce our impact on nature.”
Lough Carra was once one of Europe’s finest examples of a “marl” lake. Its alkaline waters were gin-clear, low in nutrients and home to some of the rarest aquatic life in the country, including Marl Lake mayflies, rare dragonflies, freshwater crayfish, redshank, water beetles and lichens. However, the lake has been profoundly altered by excessive nutrients from slurry and fertiliser from agriculture.
In 2022, researchers from Trinity College Dublin extracted marl samples from the lake bed and discovered huge increases in nitrogen and phosphorous levels since the 1960s. The thick bed of white marl on the bottom of the lake had acted like a sponge, soaking up as much nutrients as possible, but as the phosphorous and nitrogen kept coming, it turned green. The nutrients act like fertilisers in the water, boosting algal growth (which uses up the available oxygen), reducing water transparency and plunging parts of the lake into shade.
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Local communities are trying hard to turn things around. Under a five-year EU-funded project, a group of locals, scientists, landowners and farmers are doing what they can to pull Lough Carra back from the brink of collapse. Roden and O’Connor believe that without radical and urgent changes in how we use the land, the future of our most distinctive lakes is bleak.
“There must be true integration of environmental policy, involving an acceptance that we cannot do everything everywhere.” Curbing that human instinct is, without doubt, our biggest challenge.