Blue-Green Algae: Know the Signs Before You Swim
In warm weather some lakes develop algal blooms. Some can be harmful to people and pets, so it pays to know what to look for and where to check.
What it is
So-called blue-green algae are cyanobacteria, photosynthetic bacteria found in fresh water and elsewhere. Some types can produce toxins, and blooms can appear when conditions are right.
What a bloom can look like
- Water that looks like pea soup or spilled paint.
- Scum, mats or streaks on the surface or along the shore.
- Discoloured water, often green, blue-green or brown.
What to do
- When in doubt, stay out, and keep children and pets out too.
- Do not let dogs drink from or swim in water that looks affected.
- Rinse off with clean water after swimming in any lake.
Check official advisories
Local health or environmental agencies often publish lake advisories. Check them before swimming, especially in late summer, and report suspected blooms to them.
If a person or animal becomes unwell after contact with lake water, seek medical or veterinary help and mention the exposure.
Logged 2026-10-20