Blue-green algae (also called cyanobacteria) is a type of bacteria that naturally live in lakes, rivers, and dams. Most types are harmless, but some can produce toxins that are dangerous to people, pets, and wildlife.
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- Algal blooms
An algal bloom happens when lots of algae grow quickly, making the water look blue-green, thick, or even reddish-brown. It can smell bad and look like paint or scum on the surface. Blooms can last for weeks or even months, depending on the weather and water flow.
- Use up oxygen in the water, which can kill fish and other animals.
- Can make water unsafe for drinking, swimming, recreation, or irrigation.
Look out for:
- Thick green, blue-green, or reddish-brown scum on the water
- A shiny, paint-like surface
- A strong grassy or septic smell
If you suspect a bloom:
- Stay away from the water – no swimming, fishing, or playing
- Keep pets away – don’t let them drink or swim in it
- Report it – contact the City of Casey or Melbourne Water
- Blue-Green Algae Monitoring
The City of Casey regularly monitors high-risk waterbodies for blue-green algae. If algae is found, warning signs will be placed nearby. These signs mean:
- No swimming
- No drinking the water
- No fishing or water play
- No pets in the water
Health Risks
Touching or swallowing affected water can cause:
- Sore eyes, ears, or nose
- Itchy skin or rashes
- Upset stomach (nausea, vomiting, diarrhoea)
If exposed:
- Wash with clean water straight away
- See a doctor if you feel sick
- Wash pets with fresh water
- Call a vet if your pet seems unwell
Learn More
- Department of Health – Health effects of blue-green algae
https://www.health.vic.gov.au/water/health-effects-of-blue-green-algae
- Water Quality Australia - Cyanobacteria (blue-green algae) & water quality
https://www.waterquality.gov.au/issues/blue-green-algae
Contact Us
If you think you've seen blue-green algae in a local waterbody, please let us know:
Phone: (03) 9705 5200
Email: caseycc@casey.vic.gov.au