Be Blue-Green Algae aware this summer

Date published: 24 August 2023

The public are being urged to remain vigilant and take extra care if visiting coastal areas or along river/lake areas over the summer. Blue-green algae has been found in a number of locations in Northern Ireland including Lough Neagh the Lower Bann and catchments, North Coast bathing waters and lakes in Fermanagh. The blue-green algae in Lough Neagh, confirmed on 6 June, has been moving downstream with the natural flow of water out of the lough down the River Bann, reaching the coast.

Blue Green Algae

Blue-green algae can appear in the water column or along the shoreline and can be harmful to humans and highly toxic to animals.

The Northern Ireland Environment Agency (NIEA) respond to reports of suspected algae, liaising with landowners to initiate actions as appropriate.

An NIEA spokesman said:

   “Algal blooms are naturally occurring events that are often                                associated with warmer conditions coupled with longer daylight                    hours, hence their appearance in spring and summer months.                        Although this is not always the case the blooms can be toxic and                   occur due to a wide range of complex interdependent factors.

    The public should be vigilant and adhere to any warnings not to                      enter water or let their pets come into contact with algae along the                shoreline – it can be highly toxic to animals. We are also asking the              public to report any sightings of blue-green algae to our incident                    hotline on 0800 80 70 60 or”

We are now commissioning an urgent review of existing policies to ascertain whether more can be done quickly to address current trends. We will also be setting up meetings with Department for Infrastructure, Public Health Agency, Food Standards Agency and Councils as our co-deliverers in water and fisheries management issues.

Key Blue-Green Algae facts you need to be aware of are:

  • What does Blue-Green Algae look like? During a bloom, the water becomes less clear and may look green, blue-green or greenish-brown. Scums can form during calm weather when several bloom forming species rise to the surface. This can look like paint, mousse, or small clumps. The duration of blooms may last for a few days to several weeks until conditions in the water body change and the algae die and decompose.

  • Why should you be aware of Blue-Green Algae: 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. Algal 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.

If you suspect there is blue-green algae:

  • Report it on the Bloomin Algae App: The Bloomin’ Algae App helps make reporting of blue-green algae easier and quicker, allowing environmental experts to respond faster and issue public warnings more efficiently. It enables users to submit a photo of an algae bloom on their mobile device, along with the location and activities taking place in the associated waters. Bloomin’ Algae App is free to download directly from Google Play or App Store. Find out more at the UK Centre for Ecology & Hydrology website.
  • If you don’t have Bloomin Algae App – email photos to NIEA: Report the bloom to the Northern Ireland Environment Agency. You can report any suspected blooms through our incident hotline on 0800 80 70 60 or e-mail with a photo, if possible, and details on the location of the potential bloom.
  • What happens when Blue Algae is reported: Once landowners are informed of the results and they must erect signage warning users in the area of the presence of potentially toxic blue green algae. It is the responsibility of the landowner to initiate action as it deems necessary. Follow advice provided by the landowner/operator of the river or lake.

Notes to editors: 

1. What is Blue-Green Algae? Blue-green algae is 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.

2. Roles and responsibilities

Landowners/ Operators of lakes or rivers

You must consider how your water is used when assessing risk to people and animals from exposure to blue-green algae.

You are responsible for controlling discharges of water off-site, warning users, putting up signs and restricting access. You are also responsible for deciding when restrictions can be removed. The local council also has these responsibilities for water they own.

Blue-green algal blooms and scums are natural features of some waters. Increasing shade and reducing nutrients in the water can help reduce risk of algal blooms.


Landowners or operators of lakes and rivers are responsible for managing and assessing risks associated with blue-green algae.

NIEA provides a supporting role to landowners and operators, through verifying the presence of blue-green algae through photos submitted to the Bloomin’ Algae App or directly to:, or in some cases through water samples.

It must be highlighted, that collecting and analysing a sample provides only a location specific indication of the presence or absence of algae at that point in time. NIEA will follow internal response procedures for blue-green algae.

3. Follow DAERA on Twitter at and Facebook.

4. All media queries should be directed to the DAERA Press Office: or telephone: 028 9052 4619.

5. The Executive Information Service operates an out of hours’ service for media enquiries only between 1800hrs and 0800hrs Monday to Friday and at weekends and public holidays. The duty press officer can be contacted on 028 9037 8110.

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