A search is underway for a man who dissapeared when he swam out to retrieve a drifting boat in Lake Wanaka.

Just after midday police were advised that a man was in trouble in the water on Lake Wanaka just off Stevensons Island.

Area response manager Senior Sergeant Allan Grindell said the man was on Stevensons Island when he swam out to retrieve a drifting boat but then got into trouble.

Another person swam out to help him but that person wasn't able to locate him, he said.

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Local vessels and the Coastguard started searching for him and a helicopter with paramedics on board was also assisting.

LandSAR volunteers were also helping look for the man.

A St John spokesperson confirmed a rescue helicopter had been sent to the scene.

The Police National Dive Squad had been called in and would arrive at Wanaka about midday tomorrow to assist with the search.