The wreckage of a helicopter that crashed into a deep North Canterbury lake has been found, but there's no sign of the pilot.

A remotely-operated navy submersible has been searching the bottom of Lake Sumner, about 140km northwest of Christchurch, for the helicopter which crashed on May 21 with Rangiora pilot Michael Graeme Mehrtens aboard.

Police spokesman Inspector Craig McKay told NZ Newswire an item of interest was located by the navy on Sunday evening and it was confirmed on Monday that it was the wreckage of a helicopter.

The wreckage, at a depth of 125 metres, is being searched in the hope evidence of the pilot will be found.

Insp McKay said it was too deep for divers and searchers are reliant on the navy's submersible and other technology.

Mr Mehrtens, 35, was the only person aboard the helicopter, operated by Way To Go Heliservices.