Mark Tozer, a diver of 38 years’ experience, said he was left “stunned” and “heartbroken” yesterday after going diving at the site of a shipwreck, which lies some 12km off the coast of Adelaide’s Glenelg Beach.

Tozer, who founded the Rodney Fox and Mark Tozer’s Museum and Research Centre, told 9news.com.au he had visited the shipwreck many times before, but this was the first time since a toxic algal bloom began affecting waters off parts of the state’s coast last March.

“While I was aware of the ongoing algal bloom, I had no idea of the true extent of the damage until I saw it for myself.”

In an emotional post on Facebook, Tozer said he was still struggling to process what he saw.

“‘Chernobyl’ is the word that keeps echoing in my mind,” he wrote.

“A wreck that’s normally teeming with life was stripped bare.

“No fish. No colour. Just silence. It felt like diving through a graveyard.”

The post included colourful and vibrant photos Tozer had taken just 12 months earlier at the same spot.

Tozer said the visibility at the site had been reduced to less than a few metres and dead molluscs were scattered across the sea floor.

“This is not just a beach issue,” he said.

“This environmental event is stretching far out into the ocean, affecting ecosystems that many assume are untouched.

“I strongly believe the public needs to be made aware that this crisis is not confined to the shorelines—it’s spreading deep into our marine environment.”

The  Karenia mikimotoi species of algae was first detected on the Fleurieu Peninsula in mid-March.

Metres of foam and dead fish began washing up in a stretch across Waitpinga and Parsons beaches.

Since then, foaming seas and fish kills have been seen along the Fleurieu Peninsula, Kangaroo Island and Yorke Peninsula.

Most recently, low levels of the algae have been found in West Lakes, and testing is being done in the Port River.

Karenia mikimotoi is not toxic to 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. 

Back in March, more than 100 surfers reported becoming sick with cold and allergy-like symptoms.

The algae can be devastating to marine life and affect fish gills and skin.

Fish, sharks, rays, and a wide range of invertebrates have all been impacted by the ongoing bloom.

According to the SA Department of Environment, there is nothing that can be done to dilute or dissipate the bloom naturally, and similar blooms around the world have lasted from weeks to several months.

The bloom, believed to have been caused by an ongoing marine heatwave and calm conditions, has started to clear somewhat thanks to cooler winter temperatures.

“What this species does is that when conditions are less favourable, it changes its mode of reproduction, and it ends up producing cysts, which sink to the sea floor, and they float around, and they wait, basically, in simple terms, until the conditions are better again,” he said.

“When there’s more light, more water, warm water, the appropriate salinity level, and enough nutrients, then they’ll start reproducing again.”

Rod Ness, a commercial fisherman in Victor Harbor for three decades, said last week sales at his fresh fish shop had dropped 70 per cent in the last three weeks.

The slump has prompted calls for the algal bloom to be declared a national disaster by the federal government.