The Queenstown architect won the title at the Splash Freediving New Zealand Pool Nationals held in Auckland last weekend.
Participants competed acoss three disciplines, but a strong static breath hold time of 6min 45sec secured Nevatt the women's title.
She is a former world champion in static apnoea.
The national title is decided by a combination of points from three swimming pool-based events.
In static apnoea the diver lies face-down in the water and holds their breath as long as possible.
In dynamics, a distance based event, divers swim lengths underwater in a 50m pool as far as possible on a single breath using a monofin, a large fin that resembles a mermaid's tail. Nevatt swam 181m.
Thirdly, in dynamics without fins, divers swim underwater breaststroke as far as they can on a single breath. Nevatt, a former world record holder in this event, managed 143m.