What is blue-green algae? What causes it, symptoms, is it toxic to dogs and humans - what’s happened to Lough Neagh

A toxic bacteria, that can kill a dog in as little as 15 minutes, is plaguing rivers and lakes around the UK.

Experts say there is no end in sight to the catastrophe as there is no quick fix to getting rid of the bacteria, which has been created over decades.

Blue-green algae, also known as cyanobacteria, produces toxins and is harmful to both dogs and humans.

There have been several reports of the bacteria devastating fragile aquatic ecosystems as it starves them of oxygen,and killing dogs.

Since May, the bacteria has been found in waterways at more than 60 locations across Northern Ireland.

One of the lakes affected is the UK’s largest, which supplies 40% of the water to Northern Ireland. The Lough Neagh has turned a toxic green and the problem has been ongoing there since June.

The blue-green algae in the water has been caused by a lethal combination of record high temperatures, high nutrient levels, an increase in invasive foreign zebra mussels which filter the water, and long-term neglect.

Public anger over the state of Lough Neagh is escalating and a vigil has been held with campaigners describing it as a wake for the lake. More than 100 protesters, many dressed in black, carried a coffin to the shoreline to represent their concerns that the lake is "dying" due to pollution.

Scientists at the Agri-Food and Biosciences Institute (AFBI) told BBC News that blooms in the lough were at levels not seen since the 1970s.

A spokesperson for the Department of Agriculture, Environment and Rural Affairs (DAERA) said it will “take years if not decades to solve" and a panel of experts has been formed to develop "recommendations that will put Northern Ireland on a clear pathway to achieving good water quality.”

Lake Windermere in Cumbria’s Lake District National Park, northwest England, is also being affected by the bacteria.

In June people were told to avoid going into the water and to keep pets away from the lake as the Freshwater Biological Association (FBA) warned warmer temperatures could lead to harmful toxins being released in the lake.

Now, environmentalists from the Lake District have joined forces with the UK Space Agency for a project that will aim to track inflows of harmful nutrients, including phosphorus, from sewage works, agriculture, and septic tanks. The lake will be monitored from space to crack down on its pollution levels.

Zoologist Matt Staniek had previously warned "people’s health is being put at risk" after blooms were reported in the lake in 2022.

On Wednesday (4 October), dog owners were warned to stay away from the Barton Broad in Norfolk due to blue-green algae after a sample was taken on 5 September, while dog owners going to Bedford’s Priory Country Park have also been warned over the bacteria. Bedford Borough Council confirmed it put up warning notices in the area to advise people to stay out of the water and not to allow dogs into the lake.

What is blue-green algae?

The blue-green algae is not really algae but a type of bacteria. It is found in fresh and coastal waters and needs sunlight, nutrients, and carbon dioxide to grow. It blooms when agricultural pollution like slurry and fertilisers as well as sewage meet hot temperatures and sunlight causing eutrophication.

Blue-green algae photosynthesize during the day, adding oxygen to the water, but consumes it at night. This means oxygen levels can be very low in the early morning and can suffocate fish and other creatures. When the bloom has subsided, bacteria causing the decay can also remove large amounts of oxygen.

How to spot it

It can be hard to see blue-green algae unless it has collected together, where it can often resemble foam and can be found at the edge of lakes or ponds. Wind often blows blue-green algae to the edges of ponds and lakes and higher concentrations of toxin can gather here.

Blooms of blue-green algae can cause lakes to become green, blue-green or greenish brown and several species can produce musty, earthy or grassy odours. When several bloom-forming species rise to the water surface it creates scums which can look like paint, jelly or form small clumps. Scum colour varies because algal pigments differ between species, and even within single species, it depends on the nutrient supply, light intensity and age of the bloom. Scums may be blue-green, grey-green, greenish-brown or occasionally reddish-brown.

Is it harmful to dogs and humans?

The global Centers for Disease Control (CDC) urges people to avoid harmful algae and cyanobacteria because of health concerns.

The CDC says exposure can impact human livers and kidneys. Other symptoms include stomach pain, vomiting, or diarrhoea, headache, fever, tiredness, skin, eye, nose or throat irritation and neurological symptoms such as muscle weakness or dizziness. It can also cause rashes if skin touches the bacteria.

According to the Environment Agency, there haven’t been any long-term effects or deaths but, in some cases, the illnesses were severe. Exposure to blue-green algae is often fatal and can kill a dog in as little as 15 minutes to an hour after drinking contaminated water.

Dogs who survive can be left with long-lasting health problems as harmful toxins can stop a dog’s liver from functioning correctly. Symptoms can consist of seizures or fitting, vomiting, diarrhoea, difficulty breathing, weakness, collapsing, unconsciousness, confusion or disorientation, and dribbling. If your dog has been swimming or paddling in water and they start to show any symptoms, veterinary care should be sought immediately.