Heavy rainfall and a rapid fall in water salinity are believed to be behind a sudden fish-kill event along a beach in South Australia’s south-east.

Large numbers of wobbegong and Port Jackson sharks, snapper, Australian salmon, stingrays and ling fish have washed up on Eight Mile Creek Beach, just east of Port Macdonnell. 

The marine animals started washing up on the beach around Monday at a location popular with campers. 

Primary Industries and Regions SA (PIRSA) senior biosecurity advisor Chloe McSkimming said initial reports indicated heavy rains in the region had led to Eight Mile Creek, which empties at the beach, pushing more freshwater into the ocean than normal. 

This, in turn, lowered salinity levels near the creek opening, leading to the fish deaths. 

“At the moment, most of the species involved seem to be associated with rocky reef systems,” Ms McSkimming said. 

“They’re species that don’t tend to move very far and stick to one location.”

‘Unfortunate’ deaths likely natural 

Ms McSkimming said investigators had taken samples from the fish to rule out any diseases or pests being behind the deaths. 

“So far no algal, including harmful or toxic species, have been observed in water samples,” she said. 

“We’ve also collected samples to rule out aquatic animal disease and these results are still pending.” 

More fish are expected to wash up on the beach in the coming days, with fisheries officers attending the beach throughout this week. 

Ms McSkimming said the fish deaths were “unfortunate” but also likely a natural event. 

“With increased rain you do get increased runoff from freshwater inputs into the marine environment,” she said. 

“It is an unfortunate event but with these types of scenarios it can be a natural phenomenon.”