Christchurch beach-goers need to keep an eye open for some unwanted acquaintances sharing the beach.
Hundreds of Portuguese man o'war (blue bottle) have washed up on the city's beaches and have been pestering residents.
The creatures are technically siphonophores, not jellyfish, despite their appearance.
"This is something that happens every year, and over the last week we have had reports of the blue bottles from Sumner to North Beach near New Brighton," says head ranger Kelly Hansen.
"We would just warn people to be careful around the bluebottles, as the sting is particularly painful and can be very dangerous to some people, including children."
Its painful sting raises red welts which can last several days and in some cases, can be fatal.
An ambulance should be called immediately if someone develops symptoms of a serious allergic reaction after a sting, Ms Hansen says.