Private Ross was flung from an under-inflated Zodiac as he was returning from a training exercise on the lake.
The following day, his family gathered at the lake shore.
"How do you explain our continued sense of hope that Michael was playing games and that any minute he would jump out from behind a bush and say 'got ya'," family spokesman Charles Hohaia said after today's court hearing.
In court, Private Ross's aunt Marty Rogers read a victim impact statement on behalf of all of his cousins which spoke of their hurt.
"We felt haunted by the thought of his body on the bottom of the lake," she said.
The family felt "ripped off".
"His life was taken - not by his own actions - he was robbed."
While the family were not angry at the army, they were deeply saddened by what had happened, she said.
Today's legal argument centred around whether or not the judge would make a finding of culpability.
Army lawyer Craig Ruane said it was not possible for the judge to make such a finding but Department of Labour prosecutor Saar Cohen-Ronen said the court was the only place where such a finding could be made.
"There were so many errors made that we can't identify a person or an admission that led to the death of Private Ross. The errors are systematic. They cover different levels of people."
An Army Court of Inquiry finding was damning and found widespread failures in safety protocols. The redacted version released to media today revealed that the soldiers had been given no training in the life jackets on loan from the Navy and the Zodiacs had not been maintained.
Army head Major General David Gawn told reporters that he felt embarrassed when he read the report and felt that the Army had let down every parent who had entrusted their sons and daughters with the force.
He said there were systematic failures but individuals could be held to account and could face a Military Police investigation.
General Gawn said there were 33 recommendations in the report and the Army had already employed Australian Army personnel to carry out an audit of equipment.
"Michael's death was preventable. We, the New Zealand Army, did not follow procedures we have in place," he said.
Defence Minister Jonathan Coleman acknowledged the Defence Force's guilty plea.
"This was an absolute tragedy and my thoughts are with the Ross family as they continue to mourn Michael. I know today's guilty plea will be little consolation for their devastating loss," he said.
"The Defence Force has apologised to the Ross family, and it takes full responsibility for the safety failings that led to his death."
The Defence Force's external review of health and safety would report back in a few weeks, Dr Coleman said.
Labour's defence spokesman Phil Goff said the Defence Force had no option but to plead guilty.
"The catalogue of errors that led to his death are appalling. Had any one of a number of critical mistakes been avoided his life may have been saved. His death was entirely preventable," he said.
The Ministry of Business, Innovation and Employment's Health and Safety Group, which brought the prosecution, said its investigation identified systemic safety failures around the exercise.
"This tragic accident simply should not have happened. Like any other employee, Private Ross should have been able to expect that his safety was paramount to his employer - in this case, the NZ Defence Force failed to meet its obligations to him," said Brett Murray, general manager High Hazards and Specialist Services for the ministry.
