Seven of the deaths this had been a result of diving, including snorkelling, scuba or free-diving, he said, with two of those in the Wellington region.
The five-year average was five underwater drowning deaths per year.
"These are hugely tragic events for family and friends arising out of one of favourite pastimes, more so at this time of year and our thoughts go out to all," he said.
"To avoid these from occurring, we all need to take time to consider all activities around water this coming festive season, even if it is just ensuring we are actively watching and supervising those in the water."
This was the most important safety tip, he said.
It was also important to make sure equipment and toys were appropriate for the activity taking place and to be familiar with its operation.
"If all else fails, you can save yourself by ensuring your swimming ability is right for the conditions or you are wearing a life jacket or personal flotation device," he continued.
"Plan for the worst and you won't get caught out."
The Police National Dive Squad had identified a number of common factors in dive fatalities. These included using all the available air supply, exceeding safe ascent rate and/or dive times or carrying excessive weight and becoming negatively buoyant, conducting unsafe diving activities and failing to monitor the weather.
"Part of the Police Dive Squad's role is testing equipment that has been recovered in diver deaths. Often a combination of factors leads to fatalities. The onus is on the diver themselves to recognise, maintain or manage these issues to ensure a safe diving experience.
"Our message to all water sports enthusiasts this summer is to think safety before you put your boat or yourself in the water. Be prepared and keep an eye on the weather and water conditions. If it's not looking good or you're not sure then put the gear away and have a break."
