Toxic Algae – How to Stay Safe

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Toxic Algea | Wild Survivor
How to recognise Toxic Algea and stay safe

Last summer, we published an article about the dangers of Toxic Algea, the risks it poses to health and how to avoid getting into trouble. With a new outbreak of cases fuelled by the recent hot weather, we thought it would be valuable to revisit the article we shared to help our readers make the most of the last of the summer holidays.

What is Toxic Algae and why does it matter?

We’re enjoying the longest, hottest summer in the UK for over forty years (or at least most of us are) but it does also bring problems that we are not always so familiar with. No, we’re not talking about needing three showers a day and being unable to sleep because it’s too hot, we are referring to our wildlife. Media articles are full of references and pictures of the natural landscape being scorched brown, wildfires breaking out on tinder-dry moorland and wild animals struggling to find food and water. Now the latest warnings are to avoid toxic blue-green algae blooms triggered by the heatwave. In case you have not heard of this, we thought we’d have a look at what it is and what is the risk caused by it.

What is Blue-Green Algae?

Blue-green algae is technically not algae but a group of bacteria known as cyanobacteria, named because of the colour of the bacteria. There are lots of different strains and they are found pretty much every place on earth where there is water or moisture. They cannot be seen with the naked eye but in water bodies they can clump together and make their presence visible.

What is an Algae Bloom?

An algae bloom is the natural occurrence of a rapid increase of the algae organisms within any aquatic system, whether freshwater, brackish or saltwater. Blue-green algae’s favoured conditions are prolonged spells of hot, dry weather with low rainfall, although it can occur at any time of the year. Inland in the UK, blue-green algae more commonly occurs in slow or non-flowing freshwater such as ponds and lakes. An algal bloom can have serious negative effects on the biodiversity of the area it occurs in, killing off plants and animals by out-competing for nutrients and oxygen, effectively suffocating everything else.

Signs of Blue-Green Algae Bloom in Water:

Blue-green algal blooms can be seen initially as green flakes, greenish lumps or brownish dots on the surface of the water as the bacteria clumps together. The water may look a murky blue-green, green or green-brown. It may produce green scum or a dirty looking foam which can be mistaken for sewage pollution. With the action of wind and waves, the foam often collects near the water’s edge. Some blue-green algal blooms can produce earthy or musty smells.

Why is it Toxic?

Generally, algaes are not harmful when present in normal amounts, but during blooms, blue-green algae can produce concentrated amounts of cyanotoxins. Despite the name, the cyanotoxins are not cyanide based but do include some very potent poisons. Not all blue-green algae blooms are harmful either, but it is impossible to tell just by looking at it. Algal blooms which do produce toxins are classed as Harmful Algal Blooms (HAB).


The toxins produced by cyanobacteria can be very dangerous to pets, farm animals and wildlife which comes into contact with affected water. It has frequently been the cause of fatal poisoning in dogs which have come into contact with affected water.

In humans, there are no recorded deaths or known long term health problems caused by blue-green algae in the UK, but it can cause severe, acute illness. Symptoms include: vomiting & diarrhea, skin rashes, eye irritation, fever, muscle & joint pain in people who have either swallowed or swam in affected water.

How to Avoid:

It is impossible to tell if an algal bloom is harmful or not just by looking at it, so the advice is to assume it is and avoid it. Do not touch, enter, swim in or drink the water. Keep pets and children away from the water and if you have livestock, stop their access to affected water sources too.

The Environment Agency should be notified of algal blooms and they will carry out testing as well as instruct landowners to put up notices and/or restrict access while there is a risk of harm. If you find a water body that might be affected by a harmful algal bloom and cannot see any notices or actions taken, then you can report your sighting to The Environment Agency Incident Line on: 0800 80 70 60 which is open 24/7.

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