Forest & Bird says a report on the proposed Ruataniwha irrigation dam reinforces the "well-established principle" that rivers must not be allowed to get so polluted that they cannot sustain life.
The Board of Inquiry into the Tukituki Catchment Proposal's final report has given the dam a consent, on the condition that properties irrigated by the water storage scheme meet defined nutrient leaching rates, so that nitrogen and phosphorus limits are met downstream in the Tukituki River.
Forest & Bird said if built, the dam was expected to result in an intensification of agriculture in the Hawke's Bay, which in turn would result in more nitrogen and phosphorous reaching the Tukituki River.
"This decision is a big win for the health of New Zealand's lakes and rivers.
"The report sets a strong precedent in regards to the freshwater quality standards that will implement the government's National Policy Statement on Freshwater Management," Forest & Bird advocacy manager Kevin Hackwell said.