The Navy dive squad is using sonar equipment in the search for a teenager presumed drowned in Lake Okareka, near Rotorua.
The 17-year-old was a passenger on a jetski who fell into the water when it was struck by another jetski on Saturday.
Police divers began searching on Sunday, after the Coastguard, a helicopter and 20 boats were unable to find the teenager.
The operational commander of the Navy's dive team, Trevor Leslie, says the sonar equipment will allow them to carry out a far more effective search.
He says it enables a quicker and wider area search than a diver search, which is, when there is low visibility in the lake, very slow and laborious.
Mr Leslie says the same sonar equipment was used in the search for the Tongan ferry the Princess Ashika which sank in August 2009.