My experience with this sort of thing is not related to the Waikato but many years ago a 19 yr old died on a SCUBA diving charter at the Hen and Chicks. Official search did not find him and the weather cut up badly so had to be called off.
His family asked some of us to help out with a private search the following weekend (some of us had been on the same charter with him). We worked out where he had been diving and dropped lines to mark out an initial area to search then six of us swam in parallel searching with the plan being for the group to pivot once we reached the lower line and then swim another section. We also had two divers with scooters doing "out and back" runs from the deeper line.
I found him during the first pass.
It was a tough experience. There was only a slim chance we would find him so I was kind of prepared but not actually expecting it. His family had held a memorial service during the week and once they had the body they held a full funeral - very haerd on everyone but they had closure.