guide

Blue-green algae: what it looks like and what to do

Follow official warnings and avoid contact with suspected blooms or scum; appearance alone cannot identify algae reliably.

Blue-green algae (cyanobacteria) can form blooms or scum in fresh water. It can be difficult to identify by sight, and toxins may harm people and animals. Avoid entering water where a warning is posted or a bloom is suspected; keep pets away and follow local authority advice.

DAERA advises staying out if blue-green algae may be present; GOV.UK Swim Healthy likewise advises avoiding freshwater blooms and scums. Monitoring and reporting arrangements differ across nations and many sites are not monitored. If exposure is followed by illness, seek medical advice.