Large scale, foul-smelling, blue-green algal blooms around the shores of Lough Neagh are made of bacteria primarily associated with faeces from livestock or human-effluent, new research has found.
Reducing agri-business runoff and discharge from human wastewater treatment needs to be the top priority of all stakeholders, including the Stormont government, researchers from Queen’s University Belfast said.
The new study outlines the profound ecological impact and significant environmental and public health risks that blue-green algae in Lough Neagh present.
Noxious blooms of blue-green algae covered large parts of the lough last summer and also affected other waterways and beaches in the region. The algae has returned this year.
The UK and Ireland’s largest freshwater lake provides more than 40% of Northern Ireland’s drinking water and supports Europe’s largest commercial eel fishery.
It drains around 40% of Northern Ireland’s land, of which three-quarters is agricultural.
Lead author, Dr Neil Reid at the Institute of Global Food Security, Queen’s School of Biological Sciences, said: “These results confirm Lough Neagh as ‘hypertrophic’ which is the worst category of waterway nutrient pollution, indicative of decades of agricultural, industrial and domestic runoff.
“Our results are consistent with claims of faecal contamination of Lough Neagh and its tributaries, most likely from farm livestock and human-effluent wastewater treatment plants.”
Researchers used a combination of satellite imagery, nutrient analysis, gene sequencing and toxin profiling to characterise last year’s unprecedented harmful algal bloom.
Outbreaks of aquatic toxic microalgae have emerged as a global problem in recent decades driven by nutrient enrichment, industrial discharge, modification of surface waters, climate change and invasive species.
The new study, published in the journal Environment International, found that more than 80% of the bacterial DNA recovered from algal mats in Lough Neagh belonged to potentially hazardous microbes, including E.coli, Salmonella and 11 others that cause human illness.
The study identified the cause of the bloom was a common species of freshwater cyanobacteria that produces toxins under certain conditions.
Algal growth was strongly associated with water phosphorus levels which fuelled its reproduction.
In analysing the findings, Queen’s researchers detected a large array of toxins, including a particular toxin that had not yet been discovered on the island of Ireland before.
Microcystin-LR was a specific toxin that was found to have exceeded the World Health Organisation recreational exposure limit at every sample site.
Such toxins have potential to cause harm to a human’s liver, nerves and brain, and in high doses can lead to severe illness and even death.
Dr Reid said: “No one wants our environment full of potentially nasty bacteria and harmful toxins, so we need to look forward and prioritise ecological restoration and recovery.
“Farmers are key here. Technological solutions to better use slurry, for example, through anaerobic biodigestion, as well as good on-farm wastewater management is needed urgently on most farms.
“So-called ‘nature-based solutions’ such as planting vegetation and leaving buffer strips along waterways or creating drainage swales, willow plantations and reedbeds could dramatically reduce the environmental footprint of farming avoiding any conflict with the productivity and profitability of the agriculture sector.
“Such initiatives will require government to support...” he said.
An action plan to deal with the environmental crisis at Lough Neagh was approved by the Stormont Executive last month.
Run-off of fertiliser from surrounding fields over many decades has increased the nutrients in the water, feeding the bacteria’s growth.
Along with invasive species in the form of water-clearing zebra mussels, the effects of climate change on water temperature in the lough and on our weather help create the perfect conditions for the potentially toxic algae to bloom from the depths where it has always been present.
Dr Matthew Service, from the Agri-Food and Biosciences Institute (AFBI), said blue-green algae spreads rapidly.
“It starts to double every seven to 14 days,” he said.
“So once you get to where you can see it, it’s just going to keep going until either the climatic conditions change, there’s not enough light for it to reproduce or it just simply breaks up with the autumn and winter weather.”
Again this summer, AFBI scientists have detected the algae out in the middle of Lough Neagh, showing the wind is moving the very buoyant species around and causing it to clump together - or aggregate.
Last year saw the worst bloom of blue-green algae since the mid-1970′s. The AFBI said surface temperature readings were higher than usual for the time of year, with 21C detected in 2023.
The June average in recent years had been 15C. The AFBI said the conditions could pose a risk to fish and the lough ecosystem.
