They said there was ambiguity in the consent conditions set by the board of inquiry.
There may also be supplementary questions added relating to the Tukituki Plan (Plan Change 6).
Regional council chairman Rex Graham said the council's recent review of the scheme had highlighted uncertainty around the consent conditions, and it was important this was cleared up now.
The offer was initially made to the council in early May, just before a council-commissioned review into the scheme was officially accepted.
Yesterday Fish & Game chief executive Bryce Johnson said it was in the long-term interests of Hawke's Bay to have this clarified to offset the risk of further litigation in the future.
The council was congratulated by Environmental Defence Society chief executive Gary Taylor for taking this path to clarify the workability of the scheme's consents.
It was understood the council's investment arm - the Hawke's Bay Regional Investment Company - was considering whether to join the proceedings.
The matter is expected to be dealt with by the Environment Court before the end of this year.
At present the council is awaiting the outcome of a Supreme Court hearing on a land exchange needed for the scheme to go ahead.