School holidays and the onset of daylight saving are set to tempt Aucklanders back to the beach, however public health officers are warning parents to closely watch children - and look out for toxic sea slugs.

Medical Officer of Health Dr Simon Baker said it was not known yet if the threat of toxic slugs that killed five dogs was gone from Hauraki Gulf beaches and, until it was, people should be aware of the potential dangers.

"This incident will hopefully pass, but for the time being people just need to be a little bit more cautious on any Hauraki Gulf beach than they usually would be.

"People should keep a bit of a closer eye on where their kids are, particularly the under-eights and ... toddlers, who really don't know what is good to touch and what is bad to touch," he said.

Extra care should be taken at Cheltenham and Narrow Neck Beaches in Devonport - where more than 150 sea slugs were found by authorities investigating the dog deaths.

Some of the slugs were tested and were found to contain the same potent neurotoxin, TTX, found in vomit from one of the dead dogs.

Dr Baker said there were no reports of people being poisoned.

However a council worker who collected slugs from the beach, then accidentally touched his mouth, reported tingling around the mouth.

Early symptoms of poisoning from TTX include numbness and tingling around the mouth, and nausea.

Numbness and tingling can spread to the face, tongue and other areas, along with paralysis and slurred speech.

"Look out for anything like a sea slug, which is about 10cm long ... and if you touch a sea slug look out for any symptoms ... like tingling or numbness in the tongue or around the lips," said Dr Baker.

Anyone who experienced symptoms after touching a slug should immediately see a doctor, he said.

Dr Baker added that swimming in the sea was low risk.

"But at times they [slugs] are going to be suspended a little bit in the water and people are going to put their foot down on to something slimy."

Auckland Regional Public Health Service said no sea slugs had been found for 10 days and it had been two weeks since the last dog was poisoned.

"These slugs are actually quite rare most of the time," said Dr Baker.

"It may be that we don't see sea slugs again for some time until another event like this.

"It's completely unpredictable when it's going to happen."

During August and September, at least 15 dogs suffered symptoms consistent with TTX poisoning after eating slugs at Auckland beaches.

Auckland Regional Public Health said it was unknown whether the sea slugs could clear TTX from their systems, or whether this was a one-off or a commonly occurring event.

The Department of Conservation revealed this week that the deaths of several dolphins during the same weeks as the dog deaths might never be explained.

The dolphins tested negative for TTX and other suspected toxins including domoic acid found in algae.