An invasion of jellyfish has hit the coastline in the Nelson region.
The lion's mane jellyfish are common and one of the largest of the jellyfish family, National Institute of Water and Atmospheric Research (NIWA) ecologist Ken Grange says.
"We've got one of the more common jellyfish but one of the larger ones called the lion's mane," he says.
"It has an umbrella [body shape] and then these tentacles hang down from underneath it, which are used for catching food."
The jellyfish can provide a sting to those who come in contact but don't pose any serious threat to the public.
"They'll eat plankton as well as small fish and they capture those by stinging which is why some people get some welts from touching those things," Mr Grange says.
"Most people won't worry about it at all but if they get an allergic reaction they should probably see someone about it."
Despite the risks, that didn't stop a group of local boys from getting wet and diving in.
"[For] a lot of people it won't affect them particularly on their hands and feet. It might affect lips or sensitive parts of the skin," says Mr Grange.
Luckily for the boys, the ecologist reckons there's "nothing to worry about".