Tests to reveal extent of harmful algal bloom

Preliminary water samples from West Lakes have confirmed the presence of Karenia mikimotoi, the species of algae first detected on the Fleurieu Peninsula in March.

Ongoing testing in the Port River, West Lakes and along the metropolitan coastline will help provide a clearer picture of the extent of the bloom, which is also affecting the eastern and western coastlines of Spencer Gulf, Investigator Strait near North Cape on Kangaroo Island, Troubridge Point on Yorke Peninsula, the Coorong’s North Lagoon and along the coastline from Victor Harbor to Robe.

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.

There have been multiple reports of fish deaths along the metropolitan coastline – North Haven between the river mouth and marina breakwater, Tennyson Beach, north of Grange jetty and south of Christies Beach Surf Life Saving Club – and Port Broughton after the June 24 storm.

NPWS rangers collected a dolphin carcass from Tennyson Beach on Monday, while the carcass of a great white shark also washed up on Port Broughton, Yorke Peninsula, last week.

While it is not uncommon for marine mammal carcasses to wash ashore after winter storms, both the dolphin and shark are being tested to determine if the algal bloom contributed to their deaths.

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