Search teams looking for pilot missing after a helicopter went down in an isolated north Canterbury lake have spotted a possible crash site.
It is believed the pilot was spraying for gorse for the Department of Conservation when the Robinson 22 chopper went down at the northern end of Lake Sumner yesterday.
Police said search teams sent out this morning had found an oil slick on the lake, in deep water about 150m off Breaksea Bay.
However, the helicopter had not been found.
Boats, land-based searchers, a dive squad and a helicopter were continuing to scour the area around the lake and shoreline, police said.
There have been numerous investigations into past crashes of Robinson 22s, including one last year by the Transport Accident Investigation Commission (TAIC).
An inquiry was launched after two pilots were killed in a helicopter crash in Mount Aspiring National Park in April 2011.
They were on a training flight when their Robinson 22 helicopter went down on the Arawhata Saddle at the head of the Matukituki River, about 50km northwest of Wanaka.
In October 2010, a learner pilot and his instructor were killed when the Robinson 22 chopper they were in crashed in Bluff Harbour.
Student pilot Allan Munro, 67, was believed to have been practising a simulated engine problem exercise when the chopper crashed killing him and instructor Jason Wright, 29.
Investigation results released this year said the crash was likely caused by student pilot error.
The pilot of another Robinson 22 was killed in April last year when the chopper crashed into the Mistake Basin area of the Rolleston Range.
Adrian Mayberry, 59, died at the scene.
His son-in-law, Nev Sarginson, was pulled from the wreckage alive.
