"Millions" of dead shellfish washed ashore at Waihi Beach have shocked local residents and become an internet sensation.
Jeanette McCallum was walking with a friend by the beach on Tuesday when they came across the dead bed of shellfish, as far as the eye could see.
"We just couldn't believe it. It's just so shocking," she said.
"I'd say there would have been millions.
"They were deep. So when you stood on them, you could notice you just sank down into them. They would be at least ankle deep."
Mrs McCallum took a video of the find, which has quickly become popular on Facebook. As of 3.30pm the video had been viewed more than 45,870 times with hundreds of comments.
The pipi covered a large section of sand near where the stream is by the campground down to the north end of the beach.
"It was just a mass of pipi. They still had their meat inside. They weren't empty shells. They were all dead. It's very sad," Mrs McCallum said.
She said when pipi were alive they usually remain closed. Their shells opened when they died.
Mrs McCallum believed last week's torrential rain, and resulting floodwaters might be to blame as freshwater can suffocate saltwater shellfish.
"It's a real shame. For years we haven't been able to get pipi because of the paralytic toxin ban. Finally this summer we were allowed, and this happens."
Mrs McCallum operates a yoga and reflexology centre in the area and said part of her business was sharing the beauty of the beach and she was saddened at the loss of so many shellfish. However, she was heartened to seen so many like-minded people share her feelings online.
"People who have viewed it and how everyone is so concerned. It's rather lovely to realise how concerned about our environment people are."
On Facebook Irene Horne said the incident was "awful" but thanked Ms McCallum for sharing. Others commented saying it was "sad", "horrible" and a "waste of food".
A Ministry of Primary Industries spokeswoman said it had only just learned of the incident and investigators would now looking into the event to try to establish what happened.
"At this time, we don't know what caused the mass mortality," she said.
"It is not uncommon for shellfish to be affected by big flooding events or issues with water quality as a result of such events."
The spokeswoman advised people who discovered mass deaths such as this to report them to its Pests and Diseases Hotline: 0800 80 99 66.
It also advised against eating any of the shellfish.
Toi Te Ora Public Health Service has not been unable to comment at this stage.