The Hawke's Bay Regional Council is urging people not to eat dead sea creatures that wash up onto the shore.
High volumes of crayfish, sea cucumbers and even some octopus are being found on the coast of Napier, which could be caused by algae using up all the oxygen in the water.
"At the moment our current working theory is that very low levels of dissolved oxygen on the sea floor is causing oxygen stress to these animals," said marine ecologist Anna Madarasz-Smith.
"If you put 30 people into a small room and shut all the doors and shut all the windows, your oxygen levels are going to go down as people are breathing and talking and respiring."
But she said there is still a lot of uncertainty around what is killing the animals.
"I would absolutely avoid eating or taking the animals.
"We have working theories at the moment but we don't definitively know.
"Until we're able to really land this, it's just unsafe to take any animals off the shore. Just leave them be."
Madarasz-Smith said the animals should be swept up by the tide, but if they start to linger and smell people should notify the council.
RNZ