Federated Farmers New Zealand has described as "flimsy'' assessments done for the Otago Regional Council on the economic impact of setting a minimum flow for the Lindis River.
Yesterday was the final day of the public hearing into the council's plan change 5A, which seeks to set minimum flow and allocation limits for the Lindis River and maximum allocation limits for the aquifers in the Bendigo-Tarras Basin.
Federated Farmers regional policy adviser (high country) Bob Douglas told the hearing his organisation accepted the need for greater control over the amount of water taken from the river for irrigation.
But he considered an economic impact report prepared by Business and Economic Research Ltd (Berl) was not "sufficiently broad'' or "robust''.
He believed the report did not sufficiently justify its conclusion the economic effect of setting a minimum flow would be "relatively small in an average year''.
Mr Douglas told the hearing the council's plan could make some farms uneconomic.
He also urged hearing panel chairwoman Gretchen Robertson and commissioners Clive Geddes and Dr Richard Allibone to consider a longer transition time to allow farmers to adjust to the plan, suggesting December 2030.
Federated Farmers South Island regional policy manager Kim Reilly also took issue with the Berl report.
She considered the council had significantly underestimated the economic impact on landowners, the community and regional economies.
She also called for a longer transition period for farmers.
Otago Fish and Game Council chief executive Niall Watson submitted historic mining rights to water from the Lindis, now used for irrigation, were over-allocated, leading to trout and native fish being stranded and preyed on.
"Eventually all aquatic life is lost, leaving dry river beds. In effect, these rivers are subjected to severe artificial droughts every single year.''
Mr Watson said the "phase-out'' period for the historic water rights was set at 30 years when the Resource Management Act came into force in 1991.
Fish and Game argued unsuccessfully at that time for a five-year phase-out period, the 30-year period granted to allow irrigators to make alternative arrangements.
Mr Watson said there had been a lot of changes in irrigation in Central Otago in the past 10 years.
"But it appears to have been aimed at irrigation expansion rather than gearing up to provide for returning water for environmental flows to Central Otago rivers.''
Mr Watson said the Lindis was important as a local fishery in its own right and nationally important because it provided spawning and rearing areas for Lake Dunstan and the Upper Clutha River.
The hearing has been adjourned.
