Poor diving practices and poor fitness are being blamed for a rise in scuba diving deaths, with nine in the past four months.
The annual average toll for the past five years has been six deaths.
Police National Dive Squad held a presentation for scuba divers in Wellington this week, and officers urged divers to stay safe for the Easter holiday.
Dive and Ski HQ training manager Claire Murphy said people were not following safe buddy practices for the entire dive.
"They might start off with a buddy, but there's buddy procedures you should follow - maybe they're not kicking in early enough, maybe there's not enough communication with the buddy before and during the dive. So it's not working well."
Ms Murphy said people with medical problems should see their doctor before diving and should ensure they were fit.