Forest and Bird says a new ruling on the proposed Ruataniwha dam in central Hawke's Bay makes it more difficult for the project to go ahead.
A board of inquiry has upheld enforceable nitrogen limits for the controversial water storage and irrigation scheme.
The Hawke's Bay Regional Council's investment company, H-BRIC said the ruling helped clarify how to comply with consent conditions and it was confident of carrying on with capital-raising.
But Kevin Hackwell of Forest and Bird said that was just spin and bluster.
He said the consent conditions would be difficult to comply with, and predicted the company would eventually pull out of the project.
In December, the High Court ruled the board had made an error of law by including a provision in its terms of consent for the project without giving interested parties a chance to comment on it.
Ordered to reconsider the matter, the board has responded by deleting that provision.
One of the groups that challenged it in the High Court, Fish and Game, said it was delighted the board appeared to have upheld the limit on nitrogen leaching.
However, the group said it needed time to study the just-released 52-page decision.
Interested parties have 10 days to respond.