An 18-year-old male recruit is in a critical condition after falling five metres during "routine training" at the Kapooka Army Recruit Training Centre on Friday morning.
Ambulance officers were called to the Australian Defence Force base outside Wagga at about 8.30am.
NSW Ambulance Service Riverina district manager Eamonn Purcell told The Daily Advertiser that the man had to be resuscitated after suffering cardiac arrest.
"This morning the ambulance service received reports that there was an 18-year-old male that had fallen down a tunnel and was partially submerged in water," he said.
"When ambulance personnel got there we found there was an 18-year-old male in that circumstance and had cardiac arrest.
"We extricated the patient from that circumstance and resuscitated him and took him to Wagga Base Hospital in a critical condition."
Mr Purcell did not have any information about the specific injuries the man might have suffered during the incident.
A Defence spokesperson said an Australian Army recruit was injured during routine training.
"The recruit was evacuated to Wagga Wagga Base Hospital and is currently receiving treatment," the spokesperson said.
"Defence has notified the recruit's family.
"The incident is currently under investigation and therefore no further information is available at this time."
A Murrumbidgee Local Health District spokesperson said the man was still in a critical condition as of midday.
The Kapooka base includes obstacle courses, high ropes courses and an abseiling wall.
The Kapooka Army Recruit Training Centre held its latest graduation 'march out' on Monday, sending off two platoons for deployment in the armed services.