Northland Health is warning the public of a toxic algal bloom in a popular fishing area in the Bay of Islands.
It says tests have shown high levels of a toxic species of phytoplankton at Tapeka Point.
Health protection officers say shellfish from that area may be contaminated with a biotoxin that can cause diarrhetic shellfish poisoning.
The symptoms are diarrhoea, vomiting and abdominal pain after eating shellfish.
Northland Health says people should avoid shellfish taken from Cape Brett to the eastern point of Moturoa Island, including the Black Rocks.