Published 29 April 2026
Following reports of localised water discolouration at Koombana Bay over the Anzac weekend, the City can confirm that water sample results have been received.
Department of Water and Environmental Regulation (DWER) testing has identified the discolouration as being caused by Trichodesmium erythraeum, a naturally occurring marine cyanobacterium commonly known as ‘sea sawdust’.
This species is common in offshore waters along the WA coastline and blooms are typical for this time of year. It can cause visible water discolouration and an oil-slick like appearance.
DWER has confirmed, at the density observed the species has been assessed as posing a low to moderate risk to recreational water activities.
To clarify the City’s response and the facts of the situation: the City’s Environmental Health Team attended the site on Saturday afternoon, collected water samples for testing, and erected precautionary health warning signage at a specific location advising the public to avoid direct water contact as a safety measure while assessments were undertaken.
Koombana Bay and the beach were not closed at any point. No access restrictions or formal closure notices were issued. The precautionary signage was standard public health messaging used while water quality is being assessed.
By Sunday morning the discolouration had dissipated, and all precautionary signage was removed.
As a general precaution we continue to encourage community members to:
- Avoid contact with any water that appears discoloured or unusual
- Keep pets away from discoloured water
- Make a report via our Community Portal if you observe anything of concern
The City thanks the community for their patience while testing was undertaken. We will continue to monitor local waterways and work with DWER as needed.