Experts have warned dog walkers to be on the lookout for a toxic algae, which can be fatal to animals if ingested.
Blue-green algae spreads in 'blooms' over lakes and rivers, transforming the water into a vibrant green colour and giving it an earthy or musty smell.
Now, testing of the algae around the shore of Lough Neagh in Northern Ireland has revealed just how disgusting these blooms can be.
Much of the blooms tested were found to consist of bacteria primarily associated with faeces from livestock or human-effluent.
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.'
Experts have warned dog walkers to be on the lookout for a toxic algae, which can be fatal to animals if ingested
Testing of the algae around the shore of Lough Neagh in Northern Ireland has revealed just how disgusting these blooms can be
Health risks of the toxic algal blooms
Blue-green algae that creates the blooms are present nearly everywhere water is found, but thrive in warm, still bodies like lakes and ponds.
They also create a unique class of toxins, the impact of which on humans is only partly understood.
Long linked to animal deaths, high doses of the toxins in humans can cause liver damage and attack the nervous system.
Hundreds have been sickened by blooms in reservoirs and lakes, and officials in some areas now routinely close bodies of water used for recreation and post warning signs.
But less is known about exposure at lower doses, especially over the long term.
Small studies have linked exposure to liver cancer; one toxin is classified as a carcinogen. Others have suggested links to neurodegenerative disease.
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The new study outlines the profound ecological impact and significant environmental and public health risks that blue-green algae in Lough Neagh present.
Researchers believe that toxins in the lough could have potentially played a role in the deaths of some animals such as dogs, that entered the water during summer 2023.
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 per cent of Northern Ireland's drinking water and supports Europe's largest commercial eel fishery.
It drains around 40 per cent of Northern Ireland's land, of which three-quarters is agricultural.
Dr Reid said:'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.
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 UK and Ireland's largest freshwater lake provides more than 40 per cent of Northern Ireland's drinking water and supports Europe's largest commercial eel fishery
The new study, published in the journal Environment International, found that more than 80 per cent 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.
The study identified the cause of the bloom was a common species of freshwater cyanobacteria that produces toxins under certain conditions
Lough Neagh supplies 40 per cent of Northern Ireland's drinking water and sustains a major eel fishing industry, but it is being devastated by the algae
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 a just transition to sustainable agriculture through, for example, agri-environment scheme subsidies.
'Recent national and local political change should foster optimism that the environment and opportunities for change now exist.'
An action plan to deal with the environmental crisis at Lough Neagh was approved by the Stormont Executive last month.
WHAT IS THE DEADLY ALGAE?
Blue-green algae is a type of bacteria (called cyanobacteria) that shares some of the same characteristics as plants.
Blue-green algae exists all over the world and is found naturally in many inland waters, estuaries and the sea.
Blue-green algae generally grows in lakes, ponds, and slow-moving streams when the water is warm and enriched with nutrients like phosphorus or nitrogen.
The algae is very small and can't be seen with the naked eye unless it is concentrated into clumps.
It tends to look like green flakes, greenish bundles or brown dots in the water.
When environmental conditions are just right, blue-green algae can grow very quickly.
It is buoyant and floats to the surface, where it forms scum layers or floating mats.
An extensive growth is sometimes referred to as a bloom.
What are the health risks?
Blue-green algae is capable of producing several different toxins. People may be exposed to these toxins through contact with the skin (e.g. when swimming), through inhalation (e.g. when motor boating or water skiing), or by swallowing contaminated water.
These toxins can cause skin rashes, nausea, vomiting, stomach pains, fever and headaches.
Occasionally, the toxins can cause more serious illness such as liver and brain damage.
Children are at greater risk than adults of developing problems because of their lower body weight.
How can the health risks be minimised?
Not all blue-green algae blooms and sc*ms are toxic but it is not possible to tell from appearance and so it's best to assume they are harmful and take the following precautions:
- Do not swim in the water
- Do not swallow the water
- Avoid contact with the algae
- Do not eat fish caught from the water
- Observe and abide by any warning notices positioned around the water
Anyone who has come into contact with water containing blue-green algae should shower with fresh water immediately.
Anyone who has come into contact with affected water and has become ill should seek medical attention.
Source: Public Health Wales
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