The UK’s largest lake, Lough Neagh, is on course to record its worst year of potentially toxic algal blooms to date, as rescue plans remain deadlocked.
As a ban on eel-fishing in the lake is extended yet again, with local fishers’ incomes falling by 60% since 2023, there have so far this year been 139 detections of cyanobacteria (blue-green algae) growths recorded at the lough and its surrounding watercourses, according to a government pollution tracker. This is more than treble the number for the same point in 2024 (45). The data covers the 400 sq km freshwater lough, its tributaries, and smaller peripheral bodies of water, including Portmore Lough and Lough Gullion.
At the central water body within this vast lough, rivers and wetlands system that drains nearly half of all land in Northern Ireland, along with parts of two counties in the Irish republic, the number of detections was slightly lower than 2024’s tally. As of 25 August, there had been 35 confirmed reports, compared with 42 during the same period in 2024, according to the devolved Department of Agriculture, the Environment and Rural Affairs (DAERA).
Lough Neagh’s recurrent algal blooms, which choke aquatic life, are caused by an overload of phosphorous and nitrogen entering the lough system. Sixty two percent of these derive from agricultural sources – including farm runoff, fertilisers and animal waste, while 24% comes from creaking wastewater treatment facilities and 12% from septic tank leakage. The remaining 3-4% is thought to come from a range of industrial and household sources around the lough.
The data from Northern Ireland’s devolved government at Stormont comes as local people say this year’s blooms have been the “worst ever” within their lifetimes.
Dr Les Gornall, a slurry expert who worked at Lough Neagh’s last major laboratory, told the Guardian 2025’s algal blooms had been “much worse than last year’s – significantly worse”, both in terms of the extent of the blooms’ coverage and the “intensity of smell” they produced. These details are not measured by Stormont’s detections, Gornall added.
Researchers are still trying to pinpoint the impact of this photosynthesising bacteria on the lough’s complex ecology. But Gornall highlights that the pollution’s secondary effects, including proliferating aquatic weeds, which feed on the excess nutrients, are now visible.
Stormont has not released official statistics on phosphorus loads entering the lough system over the past 12 months, but Gornall believes a further 16,000 tonnes have gone into Lough Neagh since last year, with about 10,000 tonnes having been retained in the water column.
Despite numerous promises of action from politicians, Northern Ireland’s devolved government has struggled to make progress on tackling the reasons behind the lough’s pollution amid pushback from some farming groups – with the sector contributing more than 60% of overall phosphorus pressures – and the continued underfunding of the public wastewater system. Human sewage, from the public network and domestic septic tanks, is responsible for about 36% of phosphorus inputs.
Andrew Muir, the minister at DAERA, has urged his colleagues at Northern Ireland’s power-sharing executive to “match their words with action” and give the promised backing to measures aimed at limiting pollution inputs. Safeguarding Lough Neagh has been made a key strand of the executive’s programme for government.
“I feel like in recent months my hands have been tied behind my back because I have not had the support needed,” Muir told the Republic of Ireland’s state broadcaster, RTÉ.
Executive approval was secured belatedly last summer for an “action plan” designed to address pollution at Lough Neagh. However, 23 of the plan’s 37 points have not yet been implemented.
Some of the proposals in the Nutrients Action Programme (NAP), such as placing phosphorus limits on thousands of farms and introducing uncultivated “buffer strips”, have encountered significant political opposition at Stormont. A campaign to scrap the NAP, supported by the three major unionist parties and some Sinn Féin politicians, has prolonged consultation over the plans, which are due to be reconsidered when MLAs return from their summer recess next month.
Meanwhile, the fallout from Lough Neagh’s recurrent pollution crisis is deepening. Earlier this summer, a key fishery at the lough announced it would be extending a ban on the commercial fishing of eels – the water body’s most lucrative export catch – for the entire 2025 season. A Stormont committee heard in May that fishers’ incomes had fallen by about 60% since 2023, with no financial recompense or support package made available.
Discussions have continued with Nicholas Ashley-Cooper, the 12th Earl of Shaftesbury, who owns Lough Neagh’s bed and banks, and a number of proposals for the lough’s future management are being considered. Ashley-Cooper spoke at an event hosted by the Lough Neagh Development Trust in June in favour of a “sustainable funding” model, amid apparent interest in natural capital and green finance proposals for the lough from groups including the National Trust. “We are no longer speaking about theoretical concern,” he said. “The environmental crisis at Lough Neagh is there for all to see.”
However, local campaigners, who staged a demonstration in Antrim on Monday, argue Lough Neagh is worth more to some private interests “dead than alive”.
One attender, Patsy O’Malley Boyd, 59, said the lake was “way down the priority list” despite promises having been made by lough stakeholders. “But we’re looking at it for our children and our children’s children. I feel so sad about it. It’s like a choice – to go swimming here, to go walking – is being taken away from us.”
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