Several children have been stung as swarms of jellyfish are swept on to Wellington beaches from Cook Strait.
Mum Nicole Wijngaarden said her son Maximus, 7, was in excruciating pain after being stung by a lion's mane jellyfish at Freyberg Beach in Oriental Parade about midday yesterday.
There were screams of pain from other young children along the beach as they came into contact with "hundreds" of the gelatinous animals, she said.
"We weren't the only ones being stung. My son was in absolute agony, so we took off as soon as we could."
It took an hour for her son to calm down, after taking painkillers and antihistamine, and being soaked in white vinegar, then in a hot bath.
He left himself bleeding from scratching the itchy welts. "It wasn't pleasant at all," his mum said.
Both city and regional councils told her they could do nothing, so she wanted to warn other parents of the dangers.
A marine biologist is also warning swimmers to stay away from the creatures.
Victor Anderlini said it was common to see a lot of jellyfish this time of year. Concentrations of adults got caught up in winds coming through Cook Strait after breeding and feeding deep at sea.
At this time of year, they were "blooming" because plants and plankton, their main food source, were plentiful.
Swimmers should avoid all jellyfish, but particularly those with trailing tails.
"Don't touch them," Dr Anderlini said.
The lion's mane jellyfish, which is clear with an orange middle and tentacles, has very strong stingers. They sometimes detach from the animal and can sting swimmers coming into contact with them in the water.
A Wellington City Council spokesman said there were reports of "heaps" of people going into Freyberg Pool to get help with jellyfish stings. Councils could do little apart from advising people not to go swimming at the beach for the moment.
- The Dominion Post
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