About 30,000 tonnes of rock has fallen in a slip above Queenstown tourist hot spot the Shotover River.
A section of the river has been closed to commercial tourist operators and walkers for the past six weeks but the slip may mean jet boat operators can re-open for business, pending an engineer's report next week.
Queenstown Rafting managing director Vance Boyd said the local volunteer fire brigade and engineers have been working to help the slip happen since last Thursday.
Mr Boyd said 200 litres of water a minute was washed over and through the slip area to persuade the rock to come down.
"Yesterday afternoon we noticed more new movement in the slip and further fracturing. Then this morning a local resident heard a loud noise at about 6.30am," Mr Boyd said.
He said the heavy rain early in the morning helped and most of the rock has fallen into a chute beside the river with only one or two rocks falling into the water.