Police have found an "item of interest" during an underwater search at Lake Sumner - but do not yet know if it is the body of a pilot whose helicopter plunged into the lake last month.

Michael Graeme Mehrtens, 35, was the only occupant of a Hughes 500 helicopter that crashed near Breaksea Bay at the North Canterbury lake on May 21 while spraying weeds for the Department of Conservation.

Inspector Craig McKay said the police dive squad resumed a underwater search using a radial sonar device and located an item of interest.

"At this stage we can't say whether it is the body of Mr Mehrtens," Mr McKay said.

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"Today we are deploying a remote-operated vehicle with a manipulator arm, and hope to be able to retrieve the item."

Inspector McKay said the object was in the area where helicopter wreckage was found on the lake bed at a depth of 127m.

Bad weather last week hampered the search.

The access road to the lake was cleared of snow on Saturday, allowing the police divers to resume the search yesterday.

- Herald Online