About 150 bluebottle jellyfish have been picked up in one day by a Campbells Bay resident.
Bluebottles are the most likely species to cause stings and are dangerous even when they are washed up on the beach.
The resident says it is unusual to see such a large number at one time.
"We get five to seven, maybe once a year."
She says people should be aware.
"It's been so hot, everybody's been swimming. They're quite noticeable on the beach, but in the water they're very hard to see."
Medical officer of health Dr Simon Baker says the Auckland Regional Public Health Service (ARPHS) hardly ever gets calls about bluebottles because people know to avoid them.
"The main problem for us is the tiny jellyfish that get caught in people's togs."
The bluebottle is not a true jellyfish, but a siphonophore.
It is a complex colony of specialised individuals.
This means stings have to be treated slightly differently from jellyfish stings.
If you get stung by a bluebottle, the ARPHS recommends:
Wash the affected area with fresh or saltwater.
Remove any tentacles or stings attached to the skin, but do not touch them with your bare hands.
Place the affected area in warm water of about 45 degrees. Do not apply methylated spirits, alcohol or vinegar because these will make the stings more painful.
- © Fairfax NZ News
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