"Delaying tactics" concerning the Ruataniwha dam has led Ikaroa-Rāwhiti MP Meka Whaitiri to claim "enough is enough".
The Labour politician said it beggars belief that the regional council and Hawke's Bay Regional Investment Company were still vague about the almost $300 million project.
"The deadline HBRIC set itself to line up the finances was November last year," she said.
"Then last week they advise that work on getting farmers to sign up to buy water is on hold until the project's investor mix becomes clearer.
"Trustpower and Ngāi Tahu pulled out nearly two years ago. When will the delaying tactics end?"
A spokeswoman for the regional council's investment company said staff are continuing to work hard on the remaining two conditions which need to be confirmed for the scheme to go ahead.
"These are finalising investors for the scheme and signing up farmers to take water from the scheme.
"At present the focus is on finalising the investors," she said.
"The first two conditions were confirmed last year.
"Consents for the scheme were confirmed in July last year, while in November council confirmed that HBRIC had a financially bankable design and construction contract for the scheme."
Ms Whaitiri also noted the speculation surrounding ACC and the New Zealand Super Fund as potential investors.
"No private interests seem to want a bar of this - do we really want to pump more public money into the scheme?" she asked.
The company's spokeswoman responded, saying that any preferred investors will be in a position to comment publicly once negotiations have been completed.
The MP said that certainty of cash flow is the key to funding the development of irrigation schemes, and that means farmer uptake of irrigation.
"Finding the necessary water uptake creates more cash flow certainty and therefore more certainty for investors, yet five years into this project HBRIC is still scrambling to find farmers to sign contracts and institutional investors," she said.
She said the reality is water pricing determines whether farmers or major investors will sign contracts, and at 26 cents per cubic metre, claiming "the cash flows aren't there".
"With all the missed deadlines, endless excuses and millions of ratepayer dollars already sunk into this scheme, when do we finally get the transparency and assurances that we all deserve?" she said.
"Enough is enough."