Federated Farmers is urging Central Hawke's Bay farmers to sign up to buy water from the Ruataniwha dam scheme immediately, warning the opportunity may be lost.
Hawke's Bay Regional Council needs to pre-sell 40 million tonnes of water for the project to proceed, but appears to be struggling to get farmers to sign up.
Federated Farmers and Irrigation New Zealand are holding a meeting in Waipawa tonight which is billed as a "now or never" chance for farmers to commit to the dam.
Hawke's Bay Federated Farmers President Will Foley said tonight's meeting will give practical examples of how irrigation can boost farming businesses.
"That's the real reason we want to hold this meeting - get those farmers along and I guess answering questions they still may have and give them perhaps some confidence they're lacking that irrigation does work."
Transparent Hawke's Bay, which was set up to scrutinise the dam project on behalf of ratepayers, says farmers are avoiding the costly scheme and the meeting smacks of desperation.
Spokesperson Pauline Elliot said the attempt to compare the proposed scheme with others around the country is flawed.
"The landscape and the climate are very different, the ownership and financial structures are very different."
Resource consent for the dam has not yet been granted and the Regional Council also still does not have any major investors after Trustpower and Ngai Tahu pulled out.
Four of the nine Hawke's Bay Regional Councillors have meanwhile released a proposal for an alternative to the Ruataniwa Dam.
Councillors Rick Barker, Peter Beaven, Tom Belford and Rex Graham say the pricing of water at 26 cents per cubic metre is too expensive and is a major reason why farmers are hesitating.
Mr Belford said their proposal would build the dam as currently planned, but cut out the proposed distribution system which includes pipes and canals - reducing the cost by half.