Environment groups are upset that rivers deemed to be "excellent for swimming" under new water quality standards could still make swimmers sick.
The National-led Government announced a target today of raising the proportion of "swimmable" rivers in New Zealand to 90 per cent by 2040, at a cost of $2 billion to central and local government and farmers.
At present, 72 per cent of rivers, streams and lakes were considered suitable for swimming. Until now, the bottom line for water quality has been safe for wading and boating, not "full immersion" or swimming.
Environment Minister Nick Smith said the "ambitious" target would return New Zealand's waterways to a standard "not seen in 50 years".
"This ambitious plan to improve the water quality in our lakes and rivers recognises that New Zealanders expect to be able to take a dip in their local river or lake without getting a nasty bug," he said.
But the Green Party's water spokeswoman Catherine Delahunty said a river with a grade of "excellent" could be "so polluted that 1 person in 20 gets sick from a waterborne disease".
The Government's new National Policy Statement for freshwater said a river was "excellent for swimming" if it only exceeded the threshold for faecal contamination less than 5 per cent of the time.
"The estimated risk of Campylobacter infection is less than 50 cases in every 1000 exposures," the statement said.
Delahunty said the standard had been redefined to allow twice as much faecal contamination in rivers deemed "swimmable", but this claim was strongly rejected by Smith.
Land and Water Forum's science director Ken Taylor said the change to water quality standards was more subtle.
He said the standards would put pressure on councils to clean up the very dirtiest rivers. But they would not put pressure on councils to maintain rivers which were already clean or to improve them to a pristine condition.
Taylor said the Government's policy was "reasonably positive" overall and "a step in the right direction".
For the first time, it has set a deadline for all livestock to be excluded from rivers.
The exclusion of stock, which had to be completed by 2030, would require 56,000km of extra fencing - enough to go around the world 1.5 times, Primary Industries Minister Nathan Guy said.
National's new rules for farmers could have risked a backlash from a core voting base in election year. The powerful lobby group Federated Farmers, however, was not immediately critical of the proposals and said they were a "useful next step for freshwater in New Zealand".
Water spokesman Chris Allen said the proposals for excluding stock from rivers "need to be practical".
"This is a critical area for us to get right," he said.
-80% of rivers safe for swimming by 2030
-90% of rivers safe for swimming by 2040
-Cost of $2b
-10,000km of rivers to be cleaned up
-56,000km of fencing required to keep stock out of rivers