The second person was pulled from the water by rescuers and died a short time later.
Police said in a statement they "would like to thank those members of the public who offered their assistance at the scene".
Anyone who witnessed this incident and has not yet spoken to police is being asked to please get in touch by phoning 105 and quoting event number P046830672.
The Kaituna River mouth opens up to the Bay of Plenty coastline about 20km east of Mount Maunganui.