Five years ago, we posted about a surge of sea foam stirred up by severe weather off the east coast of Australia that inundated several beaches. While that foam proved harmless and non-toxic, recent sea foam washing up on Australian beaches has been more problematic. 

The Guardian reports that mysterious foam on South Australian beaches is being blamed for more than 100 surfers becoming ill and for the deaths of leafy seadragons, fish, and octopuses.

Health authorities have closed Waitpinga and Parsons Beach, about 80km south of Adelaide, and say the foam could be due to a microalgal bloom driven by hot temperatures, still water, and an ongoing marine heatwave.

Surfers in the local area have complained of blurred vision, itchy eyes, and coughing and breathing difficulties.

“It’s just covered in a really heavy, dense, yellow foam, with a fair bit of green, slimy, scummy stuff on the beach at the tidelines,” local surfer Anthony Rowland said.

What is sea foam?

NOAA explains that seawater contains dissolved salts, proteins, fats, dead algae, detergents, and other pollutants, and a bunch of other bits and pieces of organic and artificial matter. If you shake… ocean water vigorously, small bubbles will form on the surface of the liquid.

Sea foam forms in this way – but on a much grander scale – when the ocean is agitated by wind and waves. Each coastal region has differing conditions governing the formation of sea foams.

Algal blooms are one common source of thick sea foams. When large blooms of algae decay offshore, great amounts of decaying algal matter often wash ashore. Foam forms as this organic matter is churned up by the surf.

Most sea foam is not harmful to humans and is often an indication of a productive ocean ecosystem. But when large harmful algal blooms decay near shore, there are potential for impacts to human health and the environment. …The resulting aerosol can irritate the eyes of beach goers and poses a health risk for those with asthma or other respiratory conditions. 

The sea foam event in Australia is believed to be due to a microalgal bloom — a harmful and toxic algal bloom caused by changes in temperature, light or rainfall.

“It is believed the event could be due to a microalgal bloom that has been driven by hot temperatures and still water and an ongoing marine heatwave, with temperatures currently 2.5 degrees warmer than usual, with little wind and small swell contributing to conditions,” an EPA spokesperson said.

South Australia Health principal water quality adviser David Cunliffe told Nine News that exposure to algae can trigger allergic reactions, including respiratory and eye irritation or skin rashes, while ingestion may lead to stomach upsets or flu-like symptoms.

“These symptoms disappear when the exposure stops or following washing in clean water,” he said. “People should avoid contact with discoloured fresh or marine water. If they do enter this water they should take care to wash in clean water afterwards.”

Ocean Watch Australia states on its website that “most sea foam is not harmful to humans and is often an indication of a productive ocean ecosystem. But when large harmful algal blooms decay near shore, there are potential for impacts to human health and the environment”.

“During blooms popping sea foam bubbles are one way that algal toxins become airborne. The resulting aerosol can irritate the eyes of beach goers and poses a health risk for those with asthma or other respiratory conditions.”

Toxic foam and dead fish force beach closures in South Australia

Thanks to Alaric Bond for contributing to this post.