By Abbas Nazil
Lough Neagh, the UK’s largest freshwater lake, is experiencing its worst year of toxic algal blooms on record, with cases of cyanobacteria detected across its waters and tributaries more than tripling compared with the same period last year.
According to a government pollution tracker, there have been 139 detections of blue-green algae so far in 2025, compared with just 45 by this time in 2024.
While the central body of the lough itself recorded a slight decrease from 42 detections last year to 35 this year, the wider catchment system — which covers 400 square kilometers and drains nearly half of Northern Ireland’s land, as well as parts of two Irish counties — has been severely affected.
The blooms, which choke aquatic life and devastate ecosystems, are largely caused by excessive phosphorus and nitrogen.
Agricultural runoff is responsible for about 62% of these nutrients, with wastewater treatment facilities contributing 24% and septic tank leakage accounting for another 12%.
Industrial and household sources make up the remaining 3-4%.
Local residents have described this summer’s outbreak as the worst in living memory.
Dr. Les Gornall, a slurry expert who previously worked at Lough Neagh’s main laboratory, confirmed that 2025’s blooms were “significantly worse” than last year in both coverage and intensity.
He warned that excess nutrients are also driving the spread of invasive aquatic weeds, compounding the ecological damage.
Gornall estimates that around 16,000 tonnes of phosphorus entered the lough in the past year, with 10,000 tonnes remaining in the water system.
Despite repeated political promises, Northern Ireland’s devolved government has made little progress in tackling the crisis.
Of the 37 measures outlined in last year’s official action plan, 23 have yet to be implemented.
Agricultural groups have pushed back strongly against proposals in the Nutrients Action Programme, which include limits on phosphorus use and buffer zones on farms.
Opposition from unionist parties and some Sinn Féin politicians has further delayed implementation.
The consequences are being felt most acutely by local fishers.
An eel-fishing ban — targeting the lough’s most valuable commercial species — has now been extended for the entire 2025 season.
A Stormont committee heard earlier this year that fishers’ incomes have fallen by around 60% since 2023, with no financial relief offered.
Political leaders acknowledge the scale of the challenge.
Andrew Muir, minister at the Department of Agriculture, Environment and Rural Affairs, urged colleagues to “match words with action” but admitted he has lacked the backing to enforce meaningful change.
Meanwhile, discussions with Nicholas Ashley-Cooper, the 12th Earl of Shaftesbury and owner of the lakebed, continue over future management models, with proposals ranging from natural capital financing to National Trust involvement.
For local campaigners, however, the lack of action feels like betrayal.
Residents staged a demonstration in Antrim, warning that Lough Neagh is being treated as expendable.
One protester, Patsy O’Malley Boyd, described the crisis as robbing future generations of the chance to enjoy the lake.
“It’s like a choice is being taken away from us,” she said, calling for urgent intervention before the lough’s decline becomes irreversible.
