Photos taken by InDaily over the weekend show piles of rotting carp carcases at Middleton Beach, with locals and tourists taking to social media to bemoan the stench.
The Department of Primary Industries and Regions said it started to receive reports of dead juvenile European carp being washed up on nearby Goolwa Beach on Thursday afternoon, with dead fish also being spotted as far south as Victor Harbor.
It says “hundreds” of dead fish have been spotted, with the likely cause being changing environmental conditions.
“Dead fish are expected to wash back to sea in coming days,” a department spokesperson told InDaily.
“PIRSA is working with local authorities and other stakeholders in the area to monitor the situation.”
The department’s biosecurity officer Giverny Rodgers told ABC Radio Adelaide this morning that during a natural flood event, floodplains become inundated with areas of shallow, warm waters that are perfect environments for carp spawning.
She said during spawning events, it is normal to see a high number of juvenile carp, but also high levels of fish mortality.
“The location of where these dead carp are turning up is where freshwater from the River (Murray) is entering into the ocean and mixing with the salt water,” she said.
“While carp can tolerate a really wide range of environmental conditions, which is what makes them such an effective pest species, they actually don’t do really well with high salinity.
“Carp have been washed out into the river mouth and into the ocean and experiencing that higher salinity in the water.
“It’s not surprising that that’s resulting in fish deaths in the juvenile carp.”
Rodgers said it was unlikely the event would cause a significant drop in the number of carp in the river system.
“It is probably not going to be enough to have a significant impact on the population as carp are a really abundant and really widespread pest species,” she said.
River Murray floodwaters entering the ocean have caused the water at Goolwa and Middleton Beaches to appear murky.
SA Health has advised there are no health risks associated with the water, but the Department of Primary Industries and Regions earlier this month closed Goolwa Beach to recreational fishing of pipis, also known as cockles, due to the detection of E. coli.
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