Competitors will finish off the race with a 21.2km run along the Rotary pathway and Marine Parade.
It is the first-year national championships have been held in Hawke's Bay.
The national championship events include the Suzuki Aquathlon National Championships which includes a 1km run and 5km bike ride, and the Suzuki Aqua Bike National Championships made up of a 2km swim and 125km bike ride.
Participants in these two events are competing to qualify to represent New Zealand at the ITU Multisport World Championships in the Netherlands this September.
This year the event will hold a kids' give it a go 300m ocean swim in addition to the 1km and 2km swims.
"The public is more than welcome to come dress-up, watch, and cheer on our participants.
"It'll have a great and fun atmosphere," Event Director Bruce Richardson said.
The event is held by Triathlon Hawke's Bay with support from the Napier City Council and Triathlon New Zealand.