Environment Minister Nick Smith has rejected claims by Forest and Bird that new water quality standards exclude most New Zealand rivers.
The environmental organisation said of the 450,000km of mapped streams and rivers in New Zealand, just 10 percent would be covered by the new standards.
Its chief executive, Kevin Hague, said that contradicted Dr Smith's claim that 90 percent of the country's rivers would be swimmable by 2040.
However, Dr Smith said this claim was incorrect.
'The scale of this exclusion is vast' - Kevin Hague
Mr Hague said the new standards excluded many smaller streams that were often popular with families.
"The streams that are not covered by the government's standards are often the places that are popular with local families. While they may be too small for adults to swim in, they are frequently the safe, slow rivers and streams that are perfect for children to splash about and play in," he said.
"So the scale of this exclusion is vast. It's likely, I think, that the majority of rivers and streams that people think about in their area will not be included in those rivers and streams to which this standard applies.
"That's not what New Zealanders expect from the claims the government has made."
Mr Hague said it meant families swimming in those waterways would be at risk of contracting illness.
And he said it was not just a case of small streams being excluded.
"Of course, some of those that are being excluded are very small streams, but actually, big rivers that are popular for swimming are completely excluded from the standard."
Some of those not covered under the new standard included the Tutukaka river in Whangarei, the Orewa River in North Shore, Taupō's Okaia Stream and Wellington's Wainui Stream, he said.
Just four percent of the waterways that flowed into Lake Rotorua would be covered, he said.
Creeks feed into larger waterways that are assessed - Smith
Dr Smith said the new national policy statement requires regional councils to improve water quality applies to every stream, lake and watercourse across the country.
Dr Smith said the 90 percent of streams and rivers Forest and Bird was talking about feed into the bigger rivers and lakes that would be assessed.
And he said it was unreasonable to expect the government to provide specific guidance on every one of New Zealand's thousands of streams.
"This is a question about how much does the central government tell regional councils they must do.
"We are saying they must do it for rivers and lakes. With respect to smaller creeks and streams they need to improve them. How they improve them, to what level and to what target and monitoring is being left to the regional councils."
Regional councils will control how streams less than 40cm deep are to be looked after, Dr Smith said.