Blue-Green Algae in Lough Neagh

There have been reports of blue green algae in Lough Neagh, with it becoming thick and sludgy in places. The current condition in the Lough is unusual in that these blue-green algae have not been abundant there since the mid-1970s. 

What is blue green algae?
Blue-green algae is not actually an alga but rather a type of bacteria called cyanobacteria. Cyanobacteria naturally inhabit our freshwater, coastal and marine waters and, like plants, require sunlight, nutrients and carbon dioxide to grow and reproduce. 

Cyanobacteria can increase greatly in numbers and form visible ‘algal blooms’ which can lead to poor water quality and potential toxicity. Suitable conditions for ‘blooms’ to occur include abundant sunlight, still or slow-flowing water and sufficient levels of nutrients (nitrogen and phosphorus). Algal blooms can occur throughout the year, but they are most common from May through to September when suitable weather conditions combine with a ready supply of nutrients particularly phosphorus.

Nitrogen and phosphorus are naturally present in waterways but they can also come in excessively from external sources such as agricultural fertilisers, sewage effluent, household products and storm water runoff.

The excessive toxins produced during a bloom can potentially be harmful to public health.

Blue-green algae can harm people, producing rashes after skin contact and illnesses if swallowed, or can potentially kill wild animals, livestock and pets if ingested.

Algae blooms also block sunlight from reaching other plants in the water, use up oxygen in the water at night and when decaying and hence can suffocate fish and other creatures.

The algae normally ’blooms’ over several days, but in some conditions it could last for several weeks.

The wind can blow the blooms around the water surface which can create a thicker concentration on the shores and narrower rivers and streams. Sometimes it is thick enough to create ‘mats’ of the algae.

The blue-green algae naturally dies back when the level of nutrients in the water decreases, as the algae feed on the nutrients.

What is causing the Blue Green algae?
The bacteria that creates the blue green algae feeds off nutrients in the water. Sometimes these nutrients are increased due to other factors, which in turn creates a larger blue green algae problem.

Things that could be creating excess nutrients.

Some excess fertiliser running off nearby fields used by farmers could lead to a build up of nitrogen and phosphorus.

The invasion of non-native zebra mussels, first spotted in 2005, has resulted in clearer waters in Lough Neagh. The mussels filter particles allowing light to penetrate further into the depths which encourages the growth of nuisance plants and increases the nutrients for the 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.

Anyone using equipment such as boats, kayaks, canoes or paddle boards, as well as anglers, open water swimming or triathlons need to ‘Check, Clean, Dry’ every time we leave a lake, stream or pond, to help stop the spread of invasive plants and animals in our waters.