The pollution of Lough Neagh by sewage and agricultural waste runoff has been an issue for at least 50 years. Recently the situation has gotten so bad that areas have been screened off to prevent access to the shore area and as a precautionary measure to prevent consequent illness.

Extensive algal/bacterial mat formed around the shore at Ballyronan. Picture taken by Kevin and Maura Johnston.

The media have described the problem as being due to blue-green algae. However, that is a misnomer. The problem has been caused by the growth of algae (green) and cyanobacteria (various colours including blue).  The cyanobacterial blooms can look like foam, scum, or mats on the surface of fresh water and can be coloured blue, bright green, brown, or red. Some describe them as looking like paint floating on the water.  These bacteria grow possibly in symbiosis with the algae. Depending on the type of cyanobacteria e.g., Microcystis aeruginosa they can produce toxins that cause nausea, vomiting, diarrhoea, abdominal tenderness, pain, acute liver failure, death and much more. While neurotoxins and hepatotoxins, such as microcystin and cyanopeptolin are well-understood, members of the genus Microcystis produce large numbers of different toxins many of which are not well understood. It is likely that it is the toxins produced by the cyanobacteria that have killed the dogs and swans and have affected other larger animals.

Lough Neagh is the source of some 40% of the drinking water used in Northern Ireland and the presence of bacterial toxins is creating somewhat of a dilemma for regulatory authorities, not least because of the limited testing for microcystin let alone the at least 60 odd toxins produced by cyanobacteria.

Some cyanobacteria-toxins can be inactivated by chlorine treatment as occurs during the production of mains water. Ozone treatment is even more effective. However, if the algal and cyanobacterial blooms are extensive conventional water treatment may not be effective.

Written by Michael Mullan