Could you recognise blue-green algae?

Warm weather, more sunlight and nutrient-rich waters create ideal conditions for blue-green algae to thrive. Would you know what to look out for in your local swimming spot?

As we head into summer, warm weather, more sunlight and nutrient-rich waters create ideal conditions for blue-green algae to thrive and grow rapidly – troublesome for swimmers and pets who want to take a dip. But would you know what to look out for?

What is blue-green algae?

Algae are naturally forming, found in all water bodies and are an essential part of aquatic life. The same goes for blue-green algae.

“The algae’s ability to control its own buoyancy means that during bright sunny weather, the algae migrate to the surface layer of lakes and still waters,” says Alison Holmes, one of the Environment Agency’s Environment Monitoring Specialists based in Cumbria.

“During long periods of settled, sunny and warm weather with little or no wind, blue-green algae can multiply to such an extent that blooms can form. In the right conditions, gentle breezes can move it into bays where it’s more visible.”

But when does blue-green algae become dangerous?

“Bloom and scum forming blue-green algae can produce toxins,” says Alison. “These toxins can be harmful to people and animals. Not all blue-green algae blooms are toxic, but you can’t tell by looking at them, so it’s best to assume they are.”

“Affected water bodies may appear green, blue-green or greenish brown, and can produce musty, earthy or grassy odours,” says Alison. “Blooms can also cause foaming on the
shoreline and the water can become less clear.”

In humans, blue-green algae blooms have been known to cause rashes, eye irritation, vomiting or other illnesses if swallowed. It pays to know what to look out for and to go with your gut.

“If it doesn’t look right, move to where the water is clearer,” says Alison.

What to do if you spot an algal bloom

If you spot an algal bloom, you can report it to the Environment Agency by calling their 24/7 incident hotline on 0800 807060 or reporting it via the Blooming Algae App. Swimmers in Cumbria and Lancashire can also consult a map of confirmed blooms via the Environment Agency’s Water Hub.