The Waitaki District Council and contractor Rooney Earthmoving are using a 40-tonne digger with a 19m-long boom imported specially for the job.
The aim is to see if the entrance can be widened and deepened using a digger rather than waiting to fit into a timetable for a conventional dredge, which would also be more expensive.
Council corporate services group manager Stephen Halliwell said yesterday the council had been putting aside $100,000 a year for the past three years to dredge the harbour entrance.
If the trial was successful, the council would do the work more frequently, The channel, which would be deepened to a minimum of 4m at low tide, was marked out before Christmas.
Material excavated from the channel would be removed by truck, Mr Halliwell said.
Time taken depended on tides and weather. "It's an innovative approach to dredging," he said.
Work was being done at low tide when the digger could access a shelf at the harbour entrance to the channel at the end of Holmes Wharf.
Rooney Earthmoving has previously been involved in repairs to the harbour breakwater and protection work on the foreshore opposite the Oamaru railway station.
