The matter has been flagged by conservationists, including Forest & Bird, because the land allegedly ploughed includes habitat for nationally endangered lizards found only in Otago.
The Waitaki District Council has been unable to say how the investigation would proceed or when it would be complete, but a spokeswoman said it could continue on for a matter of weeks.
"This is a complicated and sensitive issue.
"Council officers are still working on gathering information and evidence to understand exactly what has happened and the impact," the spokeswoman said.
Forest & Bird received a handwritten letter through the post informing the environmental organisation 350ha of native tussock was cleared from a Ramrock Rd station without consent.
A further 100ha was cleared within the council’s skink management area, the anonymous informant said.
After being advised of the matter, the environmental organisation asked the council about the vegetation clearance.
The council’s regulatory manager confirmed an investigation was under way on April 24.
"We can confirm we are currently investigating the clearance of a large area of indigenous vegetation; however, as the investigation is still ongoing, we are unable to provide further details at this stage," he said at the time.
Scientists have advised nationally endangered grand skinks and Otago skinks both lived in the area.
Green skinks, kōrero geckos, McCann's skinks, grass skinks, and cryptic skinks would all have been present, the experts said.
Illegal clearance of vegetation was one of the key threats to lizards in Otago, they said.
