Sonar used to search for man's body

A high-tech sonar is helping police search for the body of a man who tried to swim ashore from a boat on Lake Rotoroa in the Nelson Lakes area on Friday.

The 27-year-old Australian man is presumed to have drowned after he jumped off the boat near Maori Stream, 55-100m from shore, about 4.45pm, Sergeant John Maxwell, of Nelson police, said.

Police search and rescue vessels, a rescue helicopter and a ground team failed to find any sign of the man despite an extensive search yesterday.

The police national dive squad was called in to look for the man's body late afternoon yesterday and recommenced their search at 8am today.

Mr Maxwell said police were being assisted by a "state-of-the-art" side-scan sonar provided by the Cawthron Institute, a local research organisation that specialises in studying freshwater ecosystems and aquaculture.

The sonar was able to look deeper than divers were able to go, he said.

"The dive squad has a limited capability. The depth that they're comfortable diving is in and around the 30m mark. The sonar equipment we've used goes to 65m," Mr Maxwell told NZPA.

The sonar was also helpful because it produced clear images of the lake bed, he said.

"It shows, on one image, what looks to be some marks caused by an anchor, so it's quite detailed."

Mr Maxwell said police were likely to wind up their search about 5pm today, and would reassess the situation if the man's body was not found.

- NZPA