Harmful algal bloom detected in Port River

Testing undertaken last week has confirmed elevated levels of the Karenia species along the metropolitan coastline, and very high levels at the Garden Island and Outer Harbor boat ramps.

This is the same species of algae first detected on the Fleurieu Peninsula in March.

State government agencies are taking weekly water samples at 17 sites across West Lakes, the Port River, the Patawalonga River and the end of four jetties at Largs Bay, Grange, Glenelg and Port Noarlunga.

The Port River is home to the Adelaide Dolphin Sanctuary, whose dolphins and their water quality are monitored regularly by National Parks and Wildlife Service (NPWS), and Flinders University in collaboration with the Environment Protection Authority.

Dolphins in the sanctuary are not believed to be at immediate risk but NPWS is investigating potential risks by monitoring water quality and undertaking algae testing.

Dolphin deaths along the metropolitan coastline are most likely associated with winter storms but NPWS is collecting the carcasses and testing them to learn as much as possible about effects on marine mammals.

The algal bloom has caused discoloured water and foam along parts of the state’s coasts and has affected various marine wildlife, including fish, sharks, rays, and a wide range of invertebrates.

Karenia mikimotoi does not cause long-term harmful effects in humans but exposure to discoloured or foamy water can cause short-term skin or eye irritation and respiratory symptoms, including coughing or shortness of breath.

The bloom occurs naturally and nothing can be done to dilute or dissipate it. Experts believe there are three plausible contributing factors causing the bloom:

• A marine heatwave that started in September 2024 – with sea temperatures about 2.5°C warmer than usual – combined with calm conditions, light winds and small swells.
• The 2022-23 River Murray flood washing extra nutrients into the sea.
• An unprecedented cold-water upwelling in summer 2023-24 that has brought nutrient-rich water to the surface.

The last notable algal bloom of this type recorded in SA was at Coffin Bay, Eyre Peninsula, in 2014. Similar blooms around the world have lasted from a week to several months, depending on wind, rain and ocean temperatures.

If you are outdoors and experience irritation, go indoors, close windows and rinse exposed skin. If symptoms are more severe or do not resolve, seek medical advice from a GP and call 000 if it is a medical emergency.

Do not eat dead fish and cockles because of decomposition and spoilage. Fish caught live are safe to eat.

People and dogs should avoid swimming or surfing in discoloured water, foam or where marine life is dead or in poor health.

Dog owners should keep their pets under effective control to prevent them eating dead or dying fish, which may cause illness.

For public health advice, visit: Water quality alerts | SA Health

For regular algal bloom updates, visit Department for Environment and Water - SA harmful algal bloom update