NIEA Says Watch For Dangers Of Blue-Green Algae

Be Blue Algae aware this summer says the NIEA

Be Blue Algae aware this summer says the NIEA

The public are being urged to remain vigilant and take extra care if visiting beaches, loughs, and rivers over the holiday period because of blue-green algae dangers.

Some waterways and areas are prone to algal blooms sauch as the River Quoile and currently, the north coast over the July holidays, particularly the Portstewart/Castlerock area may be a danger following confirmation of blue-green algae at Castlerock Beach.

Blue-green algae can be harmful to humans and is highly toxic to animals.

The Northern Ireland Environment Agency (NIEA) received a report of suspected algae at Castlerock Beach on Wednesday 5 July from DAERA samplers undertaking Bathing water testing.

A water sample has since confirmed the presence of a blue-green algae Microcystis sp which has the potential to produce harmful toxins in humans and animals such as dogs.

The National Trust and local council, as beach operators in the area, were informed of the results and erected 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.

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 inter-dependent factors.

In September 2010, the River Quoile experienced one of its occasional algal blooms which caused a fish kill. Looking on are local angler Trevor Love and Cllr Eddie Rae, the then Chair of the legacy Down District Council as Departmental staff try and pump oxygen into the water to help save the fish stocks. (Photo by Jim Masson / Down News ©)

“The public should be vigilant, especially in the Portstewart and Castlerock areas, and adhere to any warnings not to enter water or let their pets come into contact with algae along the shoreline.

“And 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 email:”

Blue-green algae have been found in 20 locations across Northern Ireland this summer and can appear along in the water column or along the shoreline.

Key Blue 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:

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.

Please take extra care if visiting or walking your dog along the coast or at a river/ lake this summer.

Please take extra care if visiting or walking your dog along the coast or at a river/ lake this summer.

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.

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.