Two windswept beaches 80km south of Adelaide have been closed to the public after locals reported “more than 100” surfers fell ill on the weekend. Their symptoms included “a sore throat, dry cough and irritated eyes” or blurred vision. Dead sea dragons, fish and octopuses have also washed up on the beaches.

Water samples have been taken for testing and health authorities suspect toxins from an algal bloom may be to blame.

But the “mysterious foam” in the water is a health hazard in its own right.

My research shows people should not go in the sea when it is foaming. These bacterial smoothies can contain more harmful pathogens than a sewage treatment plant – and you wouldn’t go swimming in sewage.

Sea foam doesn’t look dangerous. But looks can be deceiving. This foam is likely to contain a mixture of many different types of microbes and pollutants.

On beaches with lots of sea foam, people should avoid all contact with the water – and definitely avoid surfing or breathing in the contaminated water droplets in the air.

I have been studying sea foams since 2003. In 2021, my PhD student Luke Wright and I published research on our discovery of infectious disease-causing microbes in the sea foams of the Sunshine Coast in Queensland.

Named Nocardiae, these microbes are filamentous bacteria that can cause foaming in wastewater treatment plants, particularly when there’s a high load of fats, oils and greases. We now know the bacteria can cause foaming in the sea too.

We detected 32 strains of Nocardiae in samples of sea foam from beaches at Noosa and south to Caloundra.

Some of these species were new to science. So we named them Nocardia australiensis and Nocardia spumea (“spumea” meaning froth or foam).

Nocardiae bacteria are known to cause skin, lung and central nervous system infections in both humans and animals. But the infection usually only takes hold in people with weakened immune systems. The bacteria can cause abscesses in the brain, lungs and liver.

The incubation time can range between one and six months, depending on the strain of bacteria and the health status of the person involved.

This means it will take some time for people to get infected and show symptoms. Long-term medical monitoring is required to detect the condition, as it can be masked by other disease-causing microbes such as the infectious agent that causes tuberculosis.

During heavy winds, microbial spores from the soil can end up on the surface of the ocean.

If the water is polluted with floating fats and grease as well as asphaltene, motor oil and hydrocarbons, these spores soon form bacterial colonies or biofilms that go forth and multiply.

That’s because these microbes use pollution as a food source. Seawater is increasingly polluted by runoff from farmland or hard surfaces such as roads. Everything washed into the stormwater drains out to sea. During heavy storms accidental overflow from sewage systems can also occur, as Rockhampton has experienced in the past.

Algae is another food source for these microbes, as they can crack open algae cells to access the nutritious oils inside. Sea foams have been observed in northern France during algal blooms.

Warm water makes matters worse, as the warmth increases the survival rate for Nocardiae. In our laboratory on the Sunshine Coast, we were able to replicate a foaming event. We found foaming started at water temperatures of 24°C and above.

Reducing stormwater pollution will reduce the growth of sea foams. Any potential incident of infections of these surfers can raise awareness of the problem.

But sea foam can also be found in pristine environments such as national parks, where it is mostly due to oils leached from trees. We proved this fact at Noosa National Park.

In my experience on the Sunshine Coast, the council and other local authorities have been very receptive to advice on how to fix the problem. They have supported our research and also completed major upgrades at sewage treatment plants over the last 20 years.

Once there’s an outbreak in the environment it is very difficult to control. That’s because ocean is an open system, as opposed to the closed system of a sewage treatment plant, where operators can use special chemicals or mechanical equipment to break the foam down. In open sea it’s impossible. So we just have to wait for it to go away.

In this case, teams of researchers from different disciplines should come together to explore the issue. Microbiologists, marine scientists, meteorologists and chemists should team up to find out what’s going on. Ocean currents should be followed to determine where the pollutants end up.

Earlier this month Tropical Cyclone Alfred whipped up sea foam all the way along the coast from South East Queensland to northern New South Wales. I was horrified to see footage of people playing in the thick, sticky sea foam, blissfully unaware of the dangers.

But the problem is not confined to Australia, sea foam can be found at polluted beaches all over the world. Examples include India and Turkey.

I have been telling this story ever since I first observed it on the Sunshine Coast in 2003. Every time there’s a major sea foam event, the media is interested. But research support is also needed in the gaps in between. We scientists need to monitor the shorelines continuously.

As long as humanity continues to produce pollution, the problem will increase. It will also worsen as the world warms, because sea foams like it hot.

Ipek Kurtböke is Associate Professor in Microbiology, University of the Sunshine Coast

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