The NSW government is resisting calls to release the full business case for a proposed dam, which could cost both the state and federal government hundreds of millions of dollars.
The final business case for the new Dungowan Dam near Tamworth has been completed, more than two years after the initial announcement.
But the Water Minister, Tamworth MP Kevin Anderson, said the full document would not be made public to protect commercial interests.
Mr Anderson said excerpts of the business case would be included in the project's environmental impact statement, which would include both environmental and financial details.
"Yes, we will know the cost of the dam," he said.
Mr Anderson all but confirmed the cost of the dam had escalated from its original estimate of $484 million.
Documents obtained by the water consultant group Slattery and Johnson last year revealed the cost could blowout to as much as $870 million.
"It's gone up a little bit, I suspect, given the cost of everything," Mr Anderson said.
Public left 'in the dark'
The Nature Conservation Council has slammed the move to conceal the full business case, and said it was appalling the public would only have access to selected excerpts.
"The government is treating the public like mushrooms — keeping them in the dark and feeding them the bare minimum," the council's acting chief executive Jacqui Mumford said.
The dam is set to be funded in a 50-50 split between the state and federal governments.
Deputy Prime Minister and New England MP Barnaby Joyce confirmed the federal government would pay half the cost, whatever the price tag.
The state and federal governments jointly announced the Dungowan proposal in late 2019, at the height of the last drought, when much of inland NSW was under severe water restrictions.
Greens MLC Cate Faehrmann, who chaired a parliamentary inquiry into the rationale for the projects, has argued the announcement was not well thought out.
"They looked like they were decisions made in the political interest, if you like, of the state government, rather than the community's interest," Ms Faehrmann said.
