Forget about sharks - the real danger in the water this summer is small, blue and packs a real punch.
Twenty beachgoers have been treated for bluebottle stings over the past week by lifeguards patrolling Northland beaches.
The influx of bluebottles, also known as Portuguese man o' war, has been put down
to the La Nina weather pattern.
Lifeguards at Ocean Beach had given first aid to nine people suffering stings. Waipu treated six people and Ruakaka reported five. The majority of people treated were children under the age of 10 who had been stung while trying to pick them up on the beaches.
Whangarei Heads Surf Lifesaving club captain Thom Horton said a young girl was stung when she grabbed one.
Another incident at Ocean Beach over the weekend saw a boy suffer 1cm wide welts on his knee, around his leg and on his hands when he was stung while swimming.
Department of Conservation marine technical support officer Paul Bussion said bluebottles had harpoon-like stingers called nematocysts, which were released when specific cells in their tentacles were touched.
He said they were "quite poisonous" and capable of harming large fish.
"I'd certainly be keeping my children away from them. If children are out in the water, you should keep your eye out for bluebottles, as they're difficult to spot," he said.
"On the beach, do not pick them up and a good idea is for parents to identify bluebottles to their kids."
Waipu Cove Regional Lifeguard Service patrol captain Nick Tomkins said Waipu beach was scattered with the jellyfish.
"There are lots of baby ones that don't sting and then there are lots of bigger ones that do sting and really hurt," he said.
"The actual jellyfish doesn't sting, it's just their long tentacles."
According to Mr Bussion the bluebottle's tentacles can grow up to 15m long.
He was unsure how much longer the bluebottles would litter Northland beaches.
"The reason we're seeing more bluebottles is because of the La Nina, as in the easterly weather conditions, as they use their body to fill themselves with air and move with the wind and water currents to travel," he said. "It's a strong La Nina, so we can expect to see more of them."
There have been no reported deaths in New Zealand resulting from bluebottle stings.