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Three Department of Conservation staff spent much of yesterday attempting to establish a ''new line'' of track from Dredge Flat to just past Sandy Bluff on the Rees-Dart circuit after a massive landslip made the section impassable.
Doc services senior ranger Richard Kennett said parts of the track had been 90m above the river, but were now about 70m above it.
While parts of the section were safe, those had to be linked to new tracks over a distance of about 3km in what would be a ''total realignment'' of that section of the popular walking track.
It was not yet known how much that would cost, but it would be covered by funding from the department's national office, set aside for emergency repairs to tracks and facilities.
Doc partnerships ranger Chris Hankin said trampers and walkers were still able to access the Rees section of the track, but had to turn around and go back the same way, rather than completing the usual circuit.
On average, 2000 people a year walked the Rees-Dart in a multi-day circuit, with another 3000 people undertaking a day walk from either the Rees or Dart road ends, he said.
Mr Hankin advised people to heed warnings about the closure of the Dart section.
''Sometimes people see closures and think we're overreacting ... there is no way [you can get through the affected section].''
At the site yesterday viscous cement-like sediment could be seen flowing down the face of the slip into the Dart River, taking with it large rocks, with material around the site likened to quicksand.
The lake, which began forming on Saturday afternoon, had risen about half a metre since Monday, Mr Kennett said.
It would get larger, but would ''come and go'' during periods of settled dry weather and heavy rain or snowmelt.
''But, we can expect it to get bigger before we see it diminish''.
The slip had been monitored by Doc and Ngai Tahu for several years and it had been noted by GNS principal scientist Simon Cox as ''probably one of the most active slips in Otago and probably in New Zealand''.
Dr Cox did a report on the slip in 2009 and said in 1965 about 15% of the fan area at the bottom of the slip was covered in debris - by 2009 65% was covered. Since then the entire alluvial fan had been covered in debris.
GNS was now writing a second report on the slip as well as looking towards the scientific lessons that might be learned from it, such as the impact landslips might have following an Alpine Fault earthquake.