Explainer: What is causing Lough Neagh to turn green?
Paint-like water on the shores of Lough Neagh. Picture: Aodhan Roberts/Belfast Telegraph
Algal blooms in Lough Neagh, which flows out into the Atlantic Ocean near Portstewart, has turned the water green.
But what is causing the spectacle and accompanying stench?
The build up of toxic sludge is the result of large quantities of cyanobacteria which is deadly to animals and has the ability to make humans sick.
Blooms naturally occur and are often associated with warmer conditions coupled with longer daylight hours in the summer months.
However, some types of algae release toxins when they decay or degrade.
The bacteria feeds off nutrients fed into the water by excess fertiliser running off nearby fields used by farmers which has led to a build up of nitrogen and phosphorus.
These elements have caused an overgrowth of algae within a short period of time resulting in an over consumption of oxygen when the algae dies.
The blooms also block sunlight for underwater plants.
But the invasion of non-native zebra mussels, first spotted in 2005, has resulted in clearer waters in Lough Neagh.
The bivalve molluscs filter particles allowing light to penetrate further into the depths which encourages the growth of nuisance plants — and algae.
The initial spread of the mussels was slow until around 2017, when a rapid increase occurred, and today large accumulations of adult zebra mussels can be found throughout the lough.
Environmentalists hold ‘wake’ for Lough Neagh over toxic algae bloom
Combined with eutrophication — the gradual increase in the concentration of nutrients in ageing aquatic ecosystems such as lakes — this exacerbates the rapid growth of bloom. This manifests as an extensive green layer on the lough’s surface which is lethal to wildlife and birds.
It has also resulted in swimming bans and spread to smaller rivers and lakes.
It has even washed up on a number of beaches and been blamed for causing a number of dog deaths.
The extent of the problem is unusual in that blue-green blooms have not been abundant in NI since the mid-1970s.
Commercial and recreational fishers of eel, trout and pollan, have expressed concern about the possible impacts of current conditions on local fish stocks.
Sonar surveys conducted by the Agri-Fodd Biosciences Institute earlier in the summer showed that most fish are remaining in their normal habitat near the bottom of the lough — for now.
