The Green Party is exaggerating the extent of the country's water quality problems, the government says.
The party said at its annual meeting yesterday that under the National-led government, two-thirds of the country's rivers were unsafe for swimming.
Party co-leader Metiria Turei said New Zealand needed a government that would stop defending polluters.
"Government subsidies for damaging irrigation projects - like the Ruataniwha dam that will impact the Tukituki River - shows the government's refusal to protect water quality," she said.
But Environment Minister Nick Smith said water quality was measured only in areas where there were known problems, skewing the figures.
"I am confident that when that data is published it will show that some of the claims that have been made by the Greens are exaggerated.
"The preliminary advice I've had from officials act is the swimmability of our waterways is significantly worse in areas like Auckland than necessarily those areas that are farms."
Lakes like Taupō, Tekapo and Manapouri that had very good water quality were not included in the Green's statistics, he said.
Dr Smith said the government was working on getting better data.
He said advice from officials was that the swimability of waterways was significantly worse in areas like Auckland, than in farming areas.
The government also disagreed with a ban on new water storage and irrigation schemes, because well-designed schemes could deliver improved water quality, he said.
The Green Party also said it would push for a moratorium on dairy conversions as part of its efforts to improve waterways.
Dr Smith said such a moratorium would be completely unworkable.
"The limits that we have set in place as a goverment around nutrients have for very first time resulted in dairy conversions not being allowed, but they should focus on those areas where there is a problem and not over the whole country."