Lough Derg: A Paradise Lost

Restoring Lough Derg to its past glory would require a national effort, and it would take a long time to reverse the damage caused to the lake by decades of pollution, an acquatic ecologist has stated.

Dr Cilian Roden, who has worked for most of his career on lakes and the seas around Ireland, made his remarks at a public meeting on the future of Derg, organised by Green Party Local Election candidate Iva Pocock and the party's South MEP Grace O' Sullivan in Nenagh Arts Centre on Tuesday of last week.

The furthest lake downstream on the Shannon, and the largest on the river, had become “the wastepaper basket of Ireland”, Dr Roden told his attentive audience. Its problems due to pollution and the consequent impacts on its unique flora and fauna could not easily be fixed. “A lot of hard work over a long time is needed to reverse it . . . I suppose it can only be fixed when the whole Shannon Basin is fixed,” he said.

Dr Roden said addressing the pollution in the lake was a national problem due to its size and location of the lough. Being the last lake downstream on the river, it was impacted by all the pollution coming from upstream.

Increasing public awarness of what was happening to the lake and having national plans to reduce the volumes of fertiliser and sewage entering the waterway were urgent.

Dr Roden said a lot of the heritage of Derg, with its rare and wonderful species, had now disappeared after decades of excessive nutrient inflows.

“I know some people here are a bit concerned about the plan to send water from Lough Derg to Dublin. I'm afraid, at times, does Dublin know what it's trying to import?” he asked.

He said the sad thing from a naturalist's point of view is that a whole menagerie of new invasive species discovered in Derg over recent decades are the same as those found in the most polluted lakes in the western world.

“Once the decision was made - or allowed to happen - that we were going to boost phosphorous and nitrogen orders of a magnitude ten to fifteen times more than nature was used to, we were saying ‘let's destroy Lough Derg’.” Inevitably, the old eco-system of the lake was going to collapse in such a scenario.

GRAVE DAMAGE

Dr Roden said that, despite the grave damage done to the lake, things could get worse. “We are putting in very large quantities of nutrients into Lough Derg every year, and it's cumulative. It's building up and sediments are getting more and more enriched.”

He said this could result in triggering toxic algal blooms so large that they could strip the water of oxygen. “At that stage you would have an ecological disaster zone.”

What had happened to the lake was a disgrace. “With this absolutely fabulous large lake, one of the largest in western Europe, with its really exciting flora and fauna and fishery. And it has come to this.”

“Basically, if I was to sum up poor Lough Derg I’d say it has too much nutrients and there's too much water colouring which comes from peat bogs. By cutting open our raised bogs we drain a lot of the soluble content into the Shannon and into Lough Derg, where the water, far from being clear, has this reddish tinge.”

All these nutrients resulted in blooms of toxic blue-green algae at certain times of the summer.

INVASIVE SPECIES

Dr Roden said many of the native species in the lake had been replaced by a whole variety of invasive species, incuding the Zebra Mussel, The Quagga Mussel, the Asian Clam, the Bloody Red Shrimp and a plant called Water Soldier that could now be found in the lake's harbours.

The arrival of the Zebra and Quagga mussels seems to be actually helping to reduce the negative impacts of nutrients on water quality. “If you're lucky a sweeter species will come into existence that can handle this, and this is basically what's happening to Lough Derg.”

SWIMMING RISKS

He was shocked to see the emergence about two decades ago of signs erected by local authorities warning people of the risk of skin irritations if they bathed in the lake during periods of toxic blue-green algal blooms and that dogs risked dying if they drank the water.

“How is it that we sit and watch one of the most beautiful habitats we have being destroyed - but we do.”

Among the casualties of the pollution was the virtual elimination of Pollen stocks in the lake - a fish species once endemic to the Shannon.

He recalled the time spent  over 100 years ago in Derg by the self-taught Irish naturalist, Nathaniel Colgan, who camped on the various island of the lake.

The records of Colgan portrayed Derg as “a naturalist's paradise”, with all sorts of rare and interesting plants growing along the water edge. Among them was a large sunflower-like plant which grew all around the lake, but had now disappeared. Derg was the only area in Ireland or Britain where it grew. (Some can still be seen in the Botanic Garden in Dublin). “Most of what Colgan described is now gone.”

PRISTINE LAKES

One of hallmarks of the few pristine lakes left in the west of Ireland was a carpet-like cover of a species of brown algae that grew in relatively shallow waters, which left tell-tale pockmarks on the stones it grew on. He suspected that the pockmarked stones used to construct the wall of the Marquess of Clanrickarde's garden in Portumna were taken from the former pure waters of Derg. The brown algal crust that denoted pristine waters was now gone from Derg and only evident in a few remaining lakes not yet badly hit by pollution in the country.

This algae dies as a result of even slight increases in nutrient concentrations in lakes. It was one of the most sensitive indicators that eutrophication of a water body had commenced.

PROTECTED HABITAT

Dr Roden said Derg was a preserved habitat under European Union law, yet it's destruction was ongoing. It appeared love of countryside was deficient in Ireland and local authorities had no real power or funding to make a difference to the environments under their remit.

“We don't seem to have any balance. If someone can make money from something then that is the end of the argument,” Dr Roden suggested.

Iva Pocock said she was prompted to organise the meeting after being alarmed by heavy blooms of toxic blue-green algae on Lough Neagh last summer and seeing warning signs being put up by Tipperary County Council warning of the risks of swimming in the Derg during blooms.

She said a report published by the Environment Protection Agency in 2021 revealed, that of 78 water bodies surveyed in the Lower Shannon and Lough Derg, 45 were deemed to be at risk.

Recommended areas for action in the report included the Ballyfinboy River valley, the lower Nenagh River, and one of its tributaries, Clareen Stream. Lough Derg itself was also listed as being in need of restoration.

Ms Pocock said water quality in County Tipperary is rated the worst of all in the south east monitoring area, which included the north of the county.

Water quality had dropped 46 per cent over the previous twelve years up to 2021. The largest contributor to the deterioration was agriculture, but poor sewage infrastructure, forestry, industry and drainage were other factors.