What are blue-green algae?

Blue-green algae (BGA) are not actually algae but a type of bacteria, called cyanobacteria. These bacteria are so small that they can't been seen with the naked eye.

BGA have been given this name because they often look like algae when the tiny, microscopic bacteria clump together in bodies of water. 

What does it look like?

Blue green algae first develop as small green particles.

If the bloom continues, it can develop into more obvious green or turquoise wispy scum on the water surface.

Check out the UK Centre for Ecology & Hydrology website for more images.   

Why is it important to be aware of them?

BGA pose risks to public and animal health when they form blooms and scums in freshwaters in warmer summer months. They produce poisons (toxins) which may cause skin rashes and more severe symptoms if swallowed. 

Dogs are at risk if they drink the water, or lick their coat after swimming, with severe symptoms requiring very rapid vet treatment.

What can I do?

Report it: If you think you have seen BGA in the water

Bloomin' Algae app


Look out for warning signs: If you see a warning sign about BGA on any of our canals or reservoirs, please take it seriously. 

People and dogs should avoid entering the water altogether. Dog owners can get more information from the Blue Cross

If you’re a boater or you take part in water sports, always wash your hands with soap after coming into contact with the water.

What does Scottish Canals do?

When we have a verified report of BGA we follow the Scottish Government's guidance to minimise risks to public health by:

  • putting up warning signs at the location
  • adding the record to the map on the Bloomin' Algae app.
  • informing other organisations including the Scottish Environment Protection Agency and local authority Environmental Health departments.
  • undertaking a risk assessment to look at where the water discharges to, if BGA have been reported at the site before and what type of water based activities take place on site.  
  • continuing to monitor the site and working with the Scottish Environment Protection Agency to try to identify ways to reduce BGA blooms in future.