Eating shellfish contaminated by marine biotoxins, bacteria, viruses or chemicals may cause serious illness. 

Shellfish are a high-risk food because they may grow in unsafe (contaminated) water where they filter and accumulate biotoxins, bacteria, viruses, and chemicals from their surroundings. They are often eaten without being cooked. 

Biotoxins are toxins or poisons produced by algae that live in seawater and can ‘bloom’ or massively increase, when conditions are favourable.

Shellfish and seawater samples around New Zealand are regularly tested to ensure they are not contaminated with biotoxins, and public warnings are issued when shellfish are not safe to eat.

Shellfish safety in Northland - Te Tai Tokerau

Shellfish biotoxin alerts

There are four main kinds of toxic shellfish poisoning. The chemicals that cause toxic shellfish poisoning are produced by certain species of algae and released into the shellfish when they filter large numbers of algae as food.

The most common and dangerous of these types of toxic shellfish poisoning is called paralytic shellfish poisoning. The symptoms of paralytic shellfish poisoning include:

  • numbness and tingling around the mouth, face, hands or feet
  • difficulties in swallowing or breathing
  • dizziness, double vision
  • in severe cases, paralysis and not being able to breathe.

Symptoms usually occur within 12 hours of eating the contaminated shellfish.

Cooking shellfish at boiling point for several minutes will destroy most harmful bacteria and viruses, but not biotoxins or chemicals. Shellfish eaten undercooked or raw will still be risky to eat.

It's recommended you do not eat shellfish gathered from urban areas because of the risk from illegally dumped contaminants, animal waste, road runoff, industrial discharges, leaching from buried materials and sewage overflows.

Only gather shellfish from areas where the seawater is visibly clean and there are no obvious sources of contamination such as:

  • sewage outfall pipes
  • farm animals, especially at dairy farms
  • stormwater outlets, pipes or culverts
  • industrial areas
  • homes – particularly if they are on septic tanks
  • where boats may discharge on-board toilets


In addition don’t gather shellfish:

  • if there are warning signs posted
  • within 28 days of a nearby sewage overflow
  • from beaches with a history of poor water quality
  • after heavy rain and storms, as rain may flush sewage residues or farm run-off into waterways

If you get sick after eating shellfish:

NPHS - Northern Region will investigate cases of toxic shellfish poisoning, liaise with other agencies and issue public warnings, as appropriate to the nature and scale of the incident.

The Ministry for Primary Industries (MPI) tests shellfish and seawater samples regularly to check if they are contaminated with biotoxins. If marine biotoxin levels in shellfish are found to be unsafe, MPI advises the public.

General questions on environments at a particular beach can be directed to Auckland Council’s environmental health officers for the particular area (09) 3010101. There may also be related information on the Safeswim website.

Last updated 25.3.2024

For health advice call Healthline for free anytime on 0800 611 116
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