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Algal blooms

What are algae?

Algae are aquatic plants that are naturally found in our rivers, estuaries and bays. Most algae use energy from the sun to grow. They are an important part of the aquatic ecosystem providing a source of food, habitat and oxygenating water during the daylight hours.

A specific type of algae known as blue-green algae or cyanobacteria are a common seasonal occurrence in Victoria. They are a natural component of most freshwater systems, including streams and lakes but are rarer in estuaries and the sea. For more information please refer to; blue green algae.

Marine Algal Blooms in Port Phillip Bay

Marine algae occur naturally and are present year-round in all marine waters, including Port Phillip Bay. Under the right conditions, marine algae can rapidly increase to create an algal bloom. Algal blooms can develop in the days or weeks after heavy rain, particularly during periods of warm, sunny and calm weather. They generally dissipate within a few days to one to two weeks.

While marine algal blooms in Victoria are rarely harmful to swimmers or other recreational users, some people experience skin irritation after contact. People are advised to avoid contact if the water looks murky or discoloured.

Some marine algae species in Port Phillip Bay have the potential to be harmful if people consume shellfish that have accumulated the algae's toxins. Victoria’s commercial seafood is subject to regular rigorous testing and must comply with stringent food safety guidelines.

The Department of Environment, Land, Water and Planning (DELWP) is responsible for responding to marine algal blooms in Port Phillip Bay. For more information please refer to; marine algal blooms.

What you might see

  • Marine algal blooms vary in colour from red, pink, white, green or brown, and may even appear as a darker or paler patch of water compared to the surroundings.
  • From above, an algal bloom will appear as an area of distinctly discoloured water, often, but not always with a sharply defined edge.
  • A bloom that has washed onto shore may appear as foam, discoloured water, sludgy material or an oily slick floating in the shallows.

Noctiluca algal bloom in Port Phillip Bay

Noctiluca Algal Bloom. Image source: Environment Protection Authority Victoria

What you can do to protect our waterways

Avoid contact with water that looks murky or discoloured as contact may irritate skin. If contact occurs, wash with clean water. This also applies to pets.

Use the Beach Report on this site to find out about water quality at bay beaches and make informed choices about using the bay.

While most algal blooms in Port Phillip Bay do not affect fish for consumption, anglers are advised not to eat fish or shellfish from an affected area.


Report possible algal blooms, discoloured water or floating slicks to the Environment Protection Authority on 1300 372 842.

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