Thirty-five people drowned in the first two months of this year - 11 more than in January and February last year, or a 46% increase.
Water Safety New Zealand describes the increase as very discouraging.
General manager Matt Claridge says: "We know that drowning incidents will peak over the summer months as people take advantage of time away from work and the warmer weather to enjoy aquatic-based activities, but to have such a dramatic increase in terms of a comparison with last year's statistics is very discouraging."
Twelve of the 15 deaths by drowning in February occurred in the top half of the North Island, with five in Auckland, three in Bay of Plenty and two each in Northland and Waikato. Five were at beaches and four in rivers and streams.
Three children drown while unsupervised
Water Safety New Zealand is urging people to follow safety rules such as wearing a lifejacket and not swimming alone.
"People are continuing to ignore safety considerations when swimming," Mr Claridge says. "Whether it is swimming alone, swimming in areas that are obviously dangerous or beyond a person's skill level, the inevitable result is that lives are lost."
Three drownings in February were those of young children who had access to water while unsupervised.
"While we feel for the families involved," Mr Claridge says, "there is really no excuse for these incidents. Parents and caregivers must ensure that young children are appropriately supervised at all times when recreating in or near the water."