Queenstown firefighters began spraying the rock on Thursday but heavy snow forced them to stop. Yesterday they returned to the task, hoping the estimated 20,000cu m of unstable rock would fall into the gorge below.
Commercial rafting operations on the Shotover River have been suspended since the slip was first detected on July 9. A subsequent report by geotechnical engineers said the failure of the rock was "imminent".
At an extraordinary Queenstown Lakes District Council meeting last Monday, councillors voted unanimously to invoke Section 330 of the Resource Management Act, to allow Queenstown Rafting to pipe water from Shady Creek to the slip, directing it into cracks.
It was hoped the water would either lubricate the slip, accelerating its failure, or build up pressure in the cracks and force the slip from the hillside.
Queenstown Raft-ing chief executive Vance Boyd said yesterday water pumped into the cracks at the top of the slip on Thursday had now frozen solid.
"You can see it's frozen on the outside - there are icicles hanging off the rock.
"That bodes well for us because when water freezes it expands."
Mr Boyd said 25,000 litres of water was pumped through high-pressure hoses by five volunteer firefighters yesterday afternoon, their focus now turning to loose rock around the slip.
"We did manage to dislodge some good chunks of rock, which is good.
"We're still focusing at the bottom of the slip . . . we'll take that as far as we can, running water through the top."
However, Mr Boyd was cautious about how long the work might continue before the slip failed.
"We'll be working on it for probably a couple of weeks. After that time we'll be asking [a geotechnical engineer] how unstable it really is."
