A number of environmental groups have gone to the High Court in Wellington in an attempt to overturn resource consents granted to the Hawke's Bay Regional Council for the development of the Ruataniwha dam.
In August the Board of Inquiry, which considered the proposal, approved consents for the water storage scheme and associated irrigation works.
Fish and Game lawyer Royden Somerville told the Court the organisation is concerned about nitrogen levels in the water.
He said the Board of Inquiry initially found that ecosystem health should be the threshold for such levels, but the Hawke's Bay Regional Council asked for that limit to be relaxed, citing river flows and the costs involved for resource consents.
Dr Somerville said as things stand more than 600 farmers would not need a resource consent for water use.
Forest and Bird lawyer Sally Gepp told the court the board accepted a significant part of the catchment was over-allocated and imposed measures designed to manage nitrogen levels in the water.
She said it then went down a path which would increase nitrogen leaching, as long as certain measures were in place.
Ms Gepp said Forest and Bird believed that was not permissible under the requirements of the National Policy Statement on freshwater management.
The hearing before Justice Collins is set down for three days.