Beachgoers were left baffled after finding hundreds of dead anchovies washed up on the shore.
Images shared on social media showed massive numbers of Australian anchovies laid across the beach at Semaphore beach in Adelaide, Australia over the weekend.
The unusual scene was reportedly accompanied by a strong odour, and appeared before local residents at low tide.
Footage shared with the 7 News TV channel also showed fish struggling to swim in shallow water nearby.
An investigation launched by the South Australia Department of Primary Industries and Regions (PIRSA) has now established the likely cause of the incident - and it could be a potential warning sign of future problems under global warming.
The state government department believes low oxygen levels combined with high temperatures resulted in the deaths, explaining in a statement: "PIRSA staff observed murky water, and measured very low dissolved oxygen levels (~30%) and high-water temperatures (~28C) in the shallows
"Indications are the likely cause of death being a school of fish becoming trapped in a large gutter during a very low tide on a hot day leading to very low oxygen levels and high-water temperatures.
"Such water conditions are beyond the physiological tolerance for Australian anchovies."
Commercial fishing had been ruled out as a potential cause of the fish deaths by PIRSA after no evidence was found of activity in the area.
Staff were not able to take direct samples of the anchovies, however, as the incident was not reported to them directly by members of the public.
Explaining how this meant they could not reach the area in time, the department said: "As a result, by the time (department) staff attended the area, the tide had risen and carcases were not observed so fresh samples were not able to be collected for laboratory analyses"
The Australian anchovy is usually found in seas around south-east Australia and New Zealand.
