Press release: The Rivers Trust issues summer season alert about increasing toxic blue-green algae blooms in Northern Ireland water bodies

The Rivers Trust is issuing an urgent warning to the public regarding the potential presence of toxic blue-green algae blooms.

Jayne Mann


With the summer holiday season in full swing in Northern Ireland and many people now enjoying recreational activities in and around rivers, lakes and beaches, The Rivers Trust is issuing an urgent warning to the public regarding the potential presence of toxic blue-green algae blooms.

In recent weeks, the Northern Ireland Environment Agency (NIEA) has revealed 10 locations where the presence of blue-green algae has been confirmed, including Lough Neagh and the lakes in Craigavon. And this week, two of Northern Ireland’s most popular North Coast beaches have been ‘red-flagged’ by the RNLI as unsafe for swimming. This means people should not enter the water under any circumstances. Castlerock and Portstewart Strands have both tested positive for blue-green algae, which can pose serious health problems in humans and has already proved deadly to at least seven dogs in the last seven weeks.

All-Ireland Director of The Rivers Trust Mark Horton said: “Blue-green algae, also known as Cyanobacteria, is not actually an algae, but a bacterium which can pose serious risks to human and animal health and the environment. It is essential to stay informed about where these algae blooms have been recorded and take necessary precautions to ensure a safe and enjoyable holiday season.

“Stay alert when entering any water bodies and make sure you familiarise yourself with what blue-green algae looks like because it can occur anywhere and quickly and may not have been reported and recorded by the NIEA. It is important for the safety of others to report any blue-green algae that you see to the incident hotline on 0800 80 70 60.

“Blue-green algae blooms can produce toxins that are harmful to humans, animals, and aquatic life. When these toxins are present in high concentrations, they can pose risks to individuals who come into contact with contaminated water or ingest it. Exposure to blue-green algae toxins can cause symptoms such as skin rashes, eye irritation, nausea, vomiting, and in severe cases, liver, or neurological damage.”

Blue-green algae blooms can occur in lakes, ponds, rivers, and other freshwater environments, particularly during warm weather conditions. They require sunlight for photosynthesis, which is their primary source of energy. Sunlight availability in clear and shallow water bodies promotes the growth of cyanobacteria. This is why blooms are often found near the water's surface, where sunlight penetration is greatest.

These blooms can give the water a green, bluish-green, or reddish-brown appearance and may form scums or mats on the surface. While not all blue-green algae produce toxins, some can release harmful cyanotoxins into the water, posing health risks to humans, pets, and farm animals.

Mark continued: “The Rivers Trust is dismayed at the increase of these toxic algae blooms in water bodies in Northern Ireland because they are a clear and dangerous indicator of increased pollution in our rivers and marine environments. Increased nutrient levels create favourable conditions for the rapid reproduction of cyanobacteria. Excessive nutrients, particularly phosphorus and nitrogen, in the water can promote the growth of blue-green algae. These nutrients often come from human activities such as agricultural runoff, sewage discharges, and the use of fertilisers.

“Blue-green algae thrive in warm water, so during the summer months, when water temperatures rise, Cyanobacteria can proliferate more rapidly. Warmer temperatures facilitate the metabolic processes of these organisms, allowing them to grow and multiply at an accelerated rate which means this problem is only going to increase in coming years with the predicted increase rise in summer temperatures and wetter winters creating increased runoff.

“The occurrence of blue-green algae blooms in the Northern Ireland freshwater and now marine environments is a complex phenomenon influenced by multiple factors. The combination of nutrient enrichment, warm temperatures, still water conditions, sewage discharge, sunlight, and other environmental factors can create the perfect environment in which it can thrive and spread.

“When blue-green algae blooms, people and animals are denied access to the river environment, which the opposite of our mission statement because as the leading environmental charity dedicated to protecting and improving Northern Ireland, Ireland and Great Britain’s rivers and waterways, The Rivers Trust's vision is to create wild, healthy rivers enjoyed by all. That is why we are working to try to stop the combined pollution matrix that allows dangerous algae to flourish.

“We need everyone, including members of the public, to work together on long-term, catchment scale strategies to prevent the conditions where blue-green algae thrive, or we are going to be facing an increasing problem every summer which will prevent people using their local river safely.

“But at the moment, we need anyone who spots the algae to quickly alert the authorities and other river users. If you observe a suspected blue-green algae bloom, please report it immediately to the Northern Ireland Environment Agency. Provide them with details, including the location, date, and any accompanying observations or photographs.

“The NIEA is encouraging the public to get involved in citizen science and help monitor the presence of blue-green algae. The Bloomin' Algae App enables members of the public to submit a photo of the bloom taken on their phone and state what activity takes place at the location so that the potential risks to people and animals can be gauged. You can also report suspected algae sightings through the incident hotline on 0800 80 70 60 or email [email protected]

“By staying vigilant and taking necessary precautions, we can ensure a safe and enjoyable holiday season while protecting ourselves, our loved ones, our pets, and the environment. Remember, it is always better to err on the side of caution when it comes to potentially toxic blue-green algae blooms.”

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