The Wangapeka Track is closed until further notice after a slip at Labour Weekend destroyed the track and created a dam.
The rockfall from the 30-metre wide slip has created a 10-metre high dam across the river and a kilometre-long lake in the valley. The river flow, which was initially disrupted, has returned to normal levels once the water reached the top of the dam.
Tasman District Council spokesman Chris Choat said the initial assessment was that the dam was safe and warranted little concern at this stage.
"The initial opinion is that this is a natural event and as a result of it being so far into the park no major damage to land further downstream should occur."
As the water flowed over the top of the dam it would create a new natural watercourse, but this would not pose any immediate threat to landowners downstream, Mr Choat said.
As a precaution, all the residents on the council's flood warning list for the Wangapeka and Motueka valleys were called to inform them of the situation.
The situation would be monitored, he said.
The site was visited last night by the Department of Conservation and engineers and a hydrologist from the Tasman District Council.
DOC Motueka visitor assets programme manager Mark Townsend said the track was impassable because of the slip and lake it had created about 6.5km upriver from the Rolling Junction eastern end of the track.
A DOC track crew would be walking into the area today to assess options for re-routing the track across the slip and around the lake.
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