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Thousands of paua were washed up dead and dying on Kaka Point beaches last week.
Residents contacted the newspaper on Thursday after discovering the shellfish and other marine animals piled up on the shore after a heavy tide.
The "natural phenomenon" had occurred previously in 2016 and 2013, although Kaka Point residents said it "has never been this bad".
When contacted, marine experts and government agencies, including the Ministry for Primary Industries (MPI), said they were aware of the situation.
"The cause of the wash-up is not yet known, but is likely due to natural events," MPI fisheries compliance regional manager Garreth Jay said, adding that MPI had taken samples for testing.
"We know that paua do not fare well in freshwater and heavy rainfall and easterly sea conditions could have caused large amounts of freshwater from the Clutha River to be pushed into the coastal waters around Kaka Point.
"Until the cause of the wash-up is confirmed, we advise people not to gather or eat any of the washed up paua."
"Paua can handle some fluctuations in salinity, but this large input of freshwater and sediment might have been too much for them to handle. Strong easterly swells that accompanied the rain would have also played a part," she said.
"We’ve seen this at Port Molyneux in 2013 near the first set of reefs south of the Clutha, and we’ve measured low salinities all the way to Campbell’s reef in the past during flood events."
National Aquarium of New Zealand general curator Joe Woolcott said if the paua were still alive and in good shape they might be able to reattach if they made it back to suitable habitat, but too much damage or time out of the water would make recovery unlikely.
Local man Glen MacPherson said although the massive amount of dead paua was "devastating", he was cautiously hopeful for paua in the area.
"I went diving six months after the big paua wash-up in 2013 and I was surprised to see how many were still there."
-- Evelyn Thorn and Nick Brook