Blue-Green Algae (Microcystis aeruginosa)

Blue-green algae are cyanobacteria that aggregate in algal blooms, forming matts or scum on the surface of freshwater and brackish waterbodies. Algal blooms can occur due to eutrophication, often as a result of sewage or industrial waste release, and chemical runoff from farmland. Blooms contain a variety of cyanobacteria species, some of which produce toxins that can be fatal to animals and pose serious health risks to humans. Some strains of the most widely occurring species, Microcystis aeruginosa, are capable of producing the highly toxic microcystin-LR which causes irreparable damage to the liver and kidneys.  

The World Health Organisation (WHO, 2021) carried out extensive work to establish guidelines for monitoring recreational waters for the potential of harmful algal blooms (HABs) which includes guideline values for Microcystin LR (MC-LR). Total microcystins (MCs) of 24 µg/L or more should trigger alert level 1, requiring further monitoring and investigation, information for site users and, informing the relevant local authorities. The potential for toxicity can only be determined through molecular or chemical analysis. 

• It is vital biosecurity is taken into account in survey design to reduce the risk of your skin having contact with the water.
• Avoid stepping into the water – this can stir up sediment, throwing up sediment DNA and any inhibitory molecules present. Sediment may clog the filter and prevent sufficient volumes of water being filtered.
• Blooms and scums are natural annual features in some waters, but incidents of blue-green algae should be reported on the Environment Agency hotline: 0800 80 70 60 (24 hours) or in Northern Ireland to [email protected].