You might want to get out and enjoy the ocean before it gets cooler - but watch out for bluebottles.

Waipu cafe owner Lynda Gibson discovered a large Portugese Man o' War bluebottle washed up on Ruakaka Beach on Monday.

"I took a photo because I thought it was a lot larger than the ones I remember growing up," Gibson said.

Read more: Editorial: Seeing red over bluebottles on Northland's coast


"A lady I spoke to up the beach said she saw a whole lot that were dried up and dead right up by the sand dunes so obviously the king tide has brought them in," Gibson said.

Niwa researcher Dennis Gordon said the bluebottles mostly appeared on west coast beaches because of the prevailing westerlies.

"Owing to the gas-filled float, and because they cannot swim like jellyfishes, blue bottles are stuck at the sea surface and are entirely at the mercy of winds, tides and currents."

Gordon said there are usually more blue bottles in the warmer seasons.

"This summer there have been more nor'westerlies in the North Tasman sea, so one would expect more stranding on the west coast, but currents around northern North Island and down the coast of Northland will deliver them there too," he said.

Contrary to popular opinion, bluebottles are not jellyfish. Jellyfish are solitary, whereas bluebottles are colonies of a type of stinger called a siphonophore, Niwa researcher Dennis Gordon said.

"Each colony comprises a gas-filled float (instead of a jelly-like bell), underneath which is a cluster of hundreds of polyp individuals; some of these feed, some reproduce and some sting.

"The latter are tentacle-like and can stretch from 10 to 30 metres long when floating in the ocean," Gordon said.


Marine ecologist Professor Chris Battershill said the species was not a serious concern for the public, however, people prone to allergic reactions should be cautious of the stingers.

"Their tentacles can dry up but they can remain viable. There is a spear in one of the glands which work as a mechanic trigger. It can be set off when something touches them."

Professor Battershill said many people thought vinegar the best remedy to treat a sting but the best course of action is to wash the sting with warm seawater.

If you see a bluebottle
- Stay a metre away from them if you do see one in the water or washed ashore
- Keep children and dogs away from them because they can still sting after they wash ashore

What to do if you do get stung
- Remove the stinger if possible, wear gloves or a wet towel to make sure you do not get re-stung
- Washing the sting with warm seawater
- Next best thing is to wash the sting with freshwater
- Do not wash the sting with vinegar
- Keep the sting clean and do not touch or scratch it
- If you require help call 0800poison