Jellyfish invade Auckland beaches

Hydromedusa from the Pacific are tiny jellyfish are invisible in the ocean. Photo / Supplied

Beachgoers have been left with painful rashes as tiny jellyfish fill the warming waters of the Hauraki Gulf.

Aucklanders and holidaymakers looking to take advantage of this week's sunny weather are being warned to take care at all Hauraki Gulf beaches after an outbreak of swimmer's rash in the past week.

Swimmers have suffered the rash, medically known as sea bather's eruption and often falsely attributed to sea lice, at Kohimarama, Long Bay, Milford, Takapuna and Maraetai beaches.

The rash can be itchier than a severe case of chickenpox and last up to two weeks.

Simon Baker, medical officer of health at the Auckland Regional Public Health Service, said the jellyfish were too small to be seen but caused painful rashes on skin that was covered by swimsuits.

"[Victims] can be really unwell and kept awake at night with nasty itches. It can be a real nuisance."

Juley Van Der Reyden's 6-year-old son, Kellan, went swimming at Maraetai Beach on Saturday and developed a rash that was more irritable than when he had chickenpox.

"I actually cut all his fingernails so he wouldn't break the skin," Ms Van Der Reyden said. "He had on a two-piece - long rash vest and shorts - so he's got it all over his back and tummy and around his legs."

Her 3-year-old daughter, Romilly, also developed a rash around her legs.

Ms Van Der Reyden would like warning signs put up at affected beaches, but Dr Baker said the problem was likely to affect all gulf swimming spots, so this was not practical.

Luane Botha of Pohutukawa Pharmacy in Beachlands said that in the past week, about 15 customers had sought treatment for their children.

"We had a few that were really, really bad ... They had it right over their body. You can't really do much ... just something for the itch like an antihistamine."

Dr Baker said health authorities were contacting pharmacies and doctors to find out how widespread the problem was.

The microscopic jellyfish get trapped in the fabric of swimwear and tend to sting once swimmers have left the water.

Towelling-down can cause the jellyfish to sting, because they release stinging cells when put under pressure.

Children often suffer the worst reaction to the stings because of their soft skin, with hundreds to thousands of tiny red bumps forming in clusters.

A similar outbreak of sea bather's eruption occurred last February as La Nina's warm currents encouraged the spread of the jellyfish on eastern Auckland beaches.

The larvae are usually found in warm, still water and are rarely a problem at beaches with heavy surf, such as Piha.

Dr Baker said the only sure-fire way to avoid the rash was to not swim at affected beaches. But swimmers could lessen their risk by not wearing large, baggy clothing and by removing their togs on leaving the water.

Last month, thousands of jellyfish washed up on Wellington's south coast beaches, including the dangerous bluebottle or Pacific man o' war, sparking warnings from authorities.

And a swarm of bluebottles, including one with 2.5-metre-long tentacles, closed Oreti Beach, near Invercargill, this month.