The Dart Valley track in Mount Aspiring National park could be closed for the rest of the year after wild weather caused land-slips, and heavy rain and flooding washed away parts of the track.
Hillsides have slipped and trees have been washed away.
Department of Conservation services manager John Roberts said it was frustrating as it had undone months of work on the track.
"In recent months we have toiled to find a new route through very difficult country, we hoped to build a basic track around what used to be Sandy Flat, linking up with the temporary track around a new lake."
Mr Roberts said there was no point in building a new track if the same thing was going to happen again.
"We cannot start until we are confident a new track will be undisturbed, we have to acknowledge nature is in charge."
DOC ranger Chris Hankin said the damage was part of on-going issues from a landslide on the track last year.
"There was a significant land-slide in January 2014 which forced a lot of debris into the valley floor, so with heavy rain it gets swept down the valley."
"The debris has raised the river, we are surprised by how much, and that is eroding away the track."
He said the Dart Valley track was still accessible, but trampers would not be able to do the linking track.
"We were hoping to get open by early Spring, but its going to take a few months to make repairs."
Mr Hankin said repairs would cost hundreds of thousands of dollars, so may have to be done in stages
"We may have to use the Department of Conservation's emergency fund, as we have to get the track back to its original safety standard."
"We want to stress to trampers, you can not walk over the Dart River, it is impassable."
The track may remain closed until next year.