A final decision on whether to make the investment is due to be made at a council meeting on June 25, after the consultation process finishes.
A four-page document available on the council's website briefly outlines several regional, environmental, cultural and recreational benefits of the scheme but does not list any of the potential risks and disadvantages of the project listed in the 16-page statement of proposal, also available on the website.
Those risks and disadvantages include lower-than-expected uptake of water from the scheme by irrigators, environmental factors, regulatory changes and possible changes to government policy, the agricultural sector and the business environment that could affect the viability of the scheme.
Social costs could include loss of amenity values in the valley flooded to accommodate the dam, increased traffic risks in the area and increased costs to maintain local roads.
"We are supposed to be taking a relatively neutral position, pointing out the advantages, risks and opportunities that [the scheme] presents then listening to the public feedback," Mr Beaven said.
"It is hard to describe the material as being balanced."
Mr Belford, the only councillor to vote against proceeding with public consultation at a council meeting last week, said councillors raised concerns about balance when the communications plan was first outlined, and were assured they could preview key presentation material before it was finalised.
"This did not happen. The integrity of the process is now compromised," he said.
Regional Council chairman Fenton Wilson dismissed the four councillors' concerns, saying it was not the role of councillors to sign off on every document prepared by the council and he was happy with the consultation process.
Mrs Lambert said the full statement of proposal was the basis for the public consultation.
As part of the consultation, the council is holding 17 public meetings between next Tuesday and May 22. It will receive submissions and hold a hearing.