Nevatt stayed underwater for 3m 14s, making her the best in the world for results this year and third for all results in the governing body Aida's rankings.
It eclipsed her 112m effort at the Wellington Winter Championships in June, where Rounthwaite was also second.
Nevatt also reached 168m in the dynamic with fins and held for breath of 6m 19s in the static.
The women train at Breathtakers Freediving Club, which has an open evening on September 2 at Lido Aquatic Centre, Palmerston North.
"Most beginners surprise themselves and can hold their breath between about two and four minutes in their first session," said Nevatt.
"We build them up slowly and the time just disappears, so they're always surprised when we tell them how long they've been under."
For more information call 027 284 0053 or email BreathtakersFC@gmail.com.