Since the beginning of March there have been increasing reports of respiratory (breathing) issues along with eye irritations, coming from the surfers in the Victor Harbor region, on South Australia’s Fleurieu Peninsula.

This climaxed on Saturday when a small swell and hot offshore wind led most Adelaide surfers to the region's popular magnets, that being Waitpinga and Parsons beaches (the affected beaches have now been closed to the public until further notice).

A greeny/brown slick was observed by most along with a foul, sulfur like smell, while inshore brown foam started to swallow the shoreline once winds shifted onshore yesterday.

Toxic foam at Waitpinga Beach (Anthony Rowland)

Additionally there appeared to be a mass fish kill event (including weedy sea dragons, leather jackets and puffer fish) washed up along the beaches.

Regular Swellnet contributor and local Andy Smyth put a shoutout on Instagram after he started hearing multiple reports of breathing issues, persistent coughing and blurred vision.

The response he received indicates that hundreds were impacted and it’s not just isolated to those two beaches. From Tunkallila to the west and Goolwa to the east, nearly anyone (apart a small minority) in contact with the ocean has been affected.

Even those watching high from headlands above, with no contact with the water were impacted.

Fish mortalities (Anthony Rowland)

This event has all the hallmarks of a harmful micro algal bloom outbreak, one which can be toxic to both humans and fish.

South Australia has been sitting under a fairly stagnant pattern of wind and clear skies resulting in a strengthening marine heat wave event through the two gulfs, extending out into the Great Australian Bight.

Sea surface temperatures inside and just outside the gulf (extending to Encounter Bay) are 3°C above normal and the build up of hot weather last week seems to have strengthened this even further into the weekend.

Algal blooms thrive under weak winds and warm sea surface temperatures and can be observed above by chlorophyll sensors on overhead satellites.

One such pass last Friday picked up high concentrations of chlorophyll (red colour) high in Gulf St Vincent but also in Backstairs Passage between Kangaroo Island and the Fleurieu Peninsula.

Chlorophyll concentration for the 14th of March (NASA)

There have also been reports of green, fluorescent water by those crossing the passage, further strengthening the case for a harmful micro algal bloom outbreak.

The state based Environment Protection Authority have sent marine scientists down to collect samples and identify the cause of the irritation but going by the colour and a previous mass fish mortality event in 2013, it looks like an algal species named Chaetoceros coarctatus might be to blame.

Such is the toxicity of Chaetoceros coarctatus, even larger fish that feed on smaller affected species can become victim, and this would account for some deeper water fish being included in those being washed up on the Fleurieu’s shores.

If this is the case the question then becomes, when will the water and surrounding areas be safe to enter again?

It all depends on how long the warm sea surface temperatures and subdued wind lasts. An increase in the local winds and cooler temperatures would help mix and break up the algal bloom, but this doesn’t look to occur anytime this week.

Toxic foam at Waitpinga Beach (Anthony Rowland)

For now, local surfers should exercise caution and if any symptoms are experienced, remove themselves from the water and environment immediately.

We’ll provide updates once the results from the EPA testing come in.