The judge has reserved his decision at a hearing relating to consents granted to the Hawke's Bay Regional Council for the development of the Ruataniwha dam.
In August a Board of Inquiry approved consents for the water storage scheme and associated irrigation works.
Three environmental groups, including Fish and Game and the Environmental Defence Society, have been in the High Court at Wellington seeking to overturn the decision.
When submissions concluded today, Justice Collins said he understood the urgency of the matter but was unlikely to be able to deliver a decision before Christmas.
The judge said it was more likely he would deliver the judgment in February.