Risk-taking behaviour is to blame for many drowning deaths, according to Water Safety New Zealand.
Ten people, including two children, have drowned in the Christmas-New Year period.
The most recent death was that of a woman in her 70s who was found floating in a west Auckland river on Tuesday.
Water Safety New Zealand manager Matt Claridge says the tragic deaths were mostly the result of people failing to follow basic safety precautions, including supervising young children around water and not wearing life jackets in boats.
Mr Claridge says it is only luck that more people did not drown and there is no room for bravado or macho-type behaviour around water activities.
With many weeks left of summer, safety must be the first priority for everyone enjoying the water, he says.
A diving trip off the coast of Wellington nearly ended in tragedy for three men last week when their boat capsized and they endured several hours in the water.
Mr Claridge says too many children are not being taught how to swim, which will put them at a lifetime risk of death by drowning, and schools are not being adequately supported to provide swimming lessons.
The holiday period began on 24 December and ended at 6am on 5 January.