The tribunal's findings, released yesterday, recommend the existing water conservation order (WCO) on the river be amended to ban damming.
The report was the culmination of a hearing which began in May last year and considered the views of 248 submitters from all over the country.
The majority of submissions supported such an amendment, with anglers, environmental groups, gold-miners, skiers and kayakers favouring further protection of the river.
The existing WCO allowed for the possibility of hydro-electric dams on the river.
Fish and Game New Zealand and the Otago Fish and Game Council sought the change to the WCO, saying the river had outstanding characteristics not identified at the time of the 1993 WCO hearing.
Otago Fish and Game chief executive Niall Watson was "very pleased" with the decision.
The conservation order now recognised a "broad range" of natural and recreational values and the "absolute prohibition of damming and diversion" was "particularly appropriate", he said.
Forest and Bird conservation advocate Quentin Duthie said the decision was a "welcome sign" the value of the nation's distinctive wildlife should not be traded for short-term economic gain.
Applicants, regional and local government bodies, iwi authorities and submitters have 15 days to make submissions on the report to the Environment Court.
If no submissions are received in that time, Environment Minister Nick Smith will consider the report.
If submissions are received, the Environment Court will hold an inquiry and provide a report and recommendations to the minister.
Opponents of the amendment include Pioneer Generation, TrustPower, Contact Energy, the Otago Regional Council and Central Otago District Council.
Pioneer Generation chief executive Peter Dowling said last night the company was still considering the report and no decision had been made on how it would proceed.
Pioneer had been considering options for hydro schemes on the Nevis River and held the lease of the land it needed.
It had entered the tenure review process with plans to freehold the land in the "footprint" of the potential dam in exchange for other blocks to be used as public conservation land.
The Department of Conservation took a "neutral" stance on the application to amend the WCO but agreed it would not block Pioneer's potential plans for a dam on the Nevis.
The tribunal, appointed by the Ministry for the Environment, comprised Richard Fowler (chairman), Carolyn Burns and Rauru Kirikiri.
They said although evidence was given about several values or characteristics of the river said to be outstanding, the Gollum galaxiid was the only one they recognised as having outstanding value.
"... the complete prohibition of damming achieves all that is necessary to protect the outstanding characteristic of the Gollum galaxiid," they said.
It was a unique species of fish found only in the Nevis which would be threatened by any dam in its habitat.
The tribunal had to weigh up the needs of primary and secondary industry and the community, but found even if there was a case for more hydro generation, it would not prevail over the outstanding characteristic that needed to be protected - the Gollum galaxiid and its habitat.
"The point can be put more provocatively, but perhaps not as accurately: if there is a need for more hydro generation, it was not suggested that there are no other options that do not involve the eradication of a particular species from the planet, " the tribunal said.
"There was a sharp contest over the need on a national scale for further hydro development.
"It became something of a clash of the titans."
