Blue-green algae: How to spot in UK water and why is it harmful?

However, amongst the many dangers of open water such as drowning hazards, there are also harmful things that grow in the water inland and in the sea.

Although algae is a natural growth that appears in many different types of waters around the UK, some algae is dangerous to both wildlife, animals and humans.

The dangers of algae blooms on inland waters

⚠️ Take extra precautions when walking your dogs near water bodies this summer to avoid contact with blue-green algae.

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On inland waters, when the conditions are right, an ‘algae bloom’ can appear and this is when the water begins to look blue or green, sometimes even brown – this is known as blue-green algae.

A texture can also appear in the water when the weather is calm as several bloom-forming species rise to the surface which can look like paint, mousse or small clumps, reports Gov.uk.

The website says: “Cyanobacteria or ‘blue-green algae’, a type of blooming algae, can produce toxins. These toxins can kill wild animals, livestock and pets. They can also harm people, producing rashes after skin contact and illnesses if swallowed.

“Algal blooms block sunlight from reaching other plants in the water. They also use up oxygen in the water at night which can suffocate fish and other creatures. Oxygen is also used up when the bloom decays.”

Algae can form on water after periods of hot and dry weather (Image: Getty)

What algae bloom is dangerous in the sea?

In the sea, marine algae include seaweeds and microscopic plants called phytoplankton.

This type of algae bloom is usually made up of one species and can occur in summer when the growing conditions are ideal.

Some algae can harm marine creatures by producing toxins or clogging the gills of fish, according to Gov.uk.

However, blooms of toxic algae are rare in English coastal waters.

The website adds: “Some non-toxic blooms can be mistaken for sewage pollution. One of the most common bloom-forming algae in English coastal waters forms a brown, frothy scum.

“This is often blown onto the shore where it breaks down into an unpleasant brown slime that smells like sewage. This soon breaks down and disappears.”

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How can blue-green algae affect humans and animals?

Both bloom and scum forming blue-green algae can produce toxins.

“Toxin producing blooms are called Harmful Algal Blooms (HABs). These toxins can kill wild animals, farm livestock and domestic pets. Farmers and pet owners should keep their animals away from affected waters,” explains the Lake District National Park website.

It adds: “In humans, they can cause rashes after skin contact and illnesses if swallowed. Illnesses including skin rashes, eye irritation, vomiting, diarrhoea, fever and muscle and joint pain have occurred in people who’ve swallowed or swam through algal scum. These haven’t led to long-term effects or death but, in some cases, the illnesses can be severe.”

It’s important to note not all blue-green algae produces toxins, but as you can’t tell from looking at it, it’s best to avoid completely.

If you see blue-green algae you must report it to the Environment Agency, by calling 0800 80 70 60.

Do not enter, drink or swallow the water and keep children and pets away.