Healthy living

Algal blooms

What is an algal bloom?

Algal bloom

Occasionally, algae can grow very fast or ‘bloom’ into thick, visible patches near the surface of the water. Blooms do occur naturally, but excessive nutrients and certain environmental conditions can cause larger growth.

Some blooms may be referred to as ‘red tides’ because of their colour while other can look like a green mat or even an oily sheen. 

What are algae and ‘blue-green algae’?

Algae are plants with a very simple cell structure, are mostly aquatic (living on, in or near water) and usually very small (microscopic) in size.

However, some can form visible filaments (strings) and mats and some can grow quite large and appear plant-like (for example, kelp). Some algae may float or attach to rocks, shells, and other plants.

Blue-green algae, known as cyanobacteria, are actually an aquatic type of bacteria. They are microscopic but can create visible scums. They are a natural part of our rivers, marine environments and estuaries (where freshwater from rivers and streams flow into the ocean).

How can I tell if there is an algal bloom?
Are algal blooms a health hazard?
Testing for algal blooms?
Public health warnings

What if I think there may be an algal bloom?

Contact the following agencies if you think there is an algal bloom in a waterway:


Last reviewed: 02-01-2024
Acknowledgements
Environmental Health Directorate, Public Health

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