Long-awaited changes to freshwater rules will be announced by Prime Minister Bill English today, and could require rivers and streams to be cleaned up across the country.

There is speculation that the National-led Government will lift the minimum standard for freshwater quality, but not to the "swimmable" standard environmental groups have been lobbying for.

Any change in water standards will still be significant because it will likely affect farmers - National's core voting base - in an election year.

Around two-thirds of monitored freshwater sites in New Zealand remain unsafe for recreational contact, according to recent reports.

The Government's National Policy Statement on freshwater requires regional councils to ensure rivers and streams are safe for wading and boating.

The influential Land and Water Forum, which represents farming, environment, business, local government and scientific interests, has recommended the Government raise the minimum standard to make all waterways safe for swimming.

The Green Party released a 12,000-signature petition yesterday demanding the Government take up the recommendation.

New Zealanders were "tired of wading and waiting for swimmable rivers", the Greens' water spokeswoman Catherine Delahunty said.

Delahunty said a "swimmable" standard was only "a start", and reaching it would require limits on stock and fixing stormwater and sewerage systems.

Environment Minister Nick Smith has previously said he is open to strengthening the national standard, but says a "swimmable" bottom line is unworkable.

• Government needs to 'rattle its dags' on freshwater quality

He said water quality was often affected by heavy rainfall, geothermal activity or even large bird populations - though that statement has been challenged by councils and scientists.

Environment Defence Society chair Gary Taylor, whose organisation is a member of the Land and Water Forum, said higher standards needed to be pushed through with greater urgency.

"We've got to see an uplift in the pace of change," he said.

"I think the Government is still behind public aspirations for freshwater. The reform process has been going for the thick end of eight years in increments. I think we just need to rattle our dags and get on with it."

He said raising water standards could require farmers to reduce stock, fence off waterways, and reduce nitrogen and phosphorus run-off.

The Government has already signalled a national regulation for excluding dairy cattle from rivers and streams, likely to be introduced in the middle of this year. It will be limited to lowlands and flat land, not high country.

At present, farmers are being encouraged to fence off streams on a voluntary basis. The Ministry for Primary Industries has estimated that 95 per cent of dairy herds were now excluded from waterways.

The Land and Water Forum wants all livestock fenced off from rivers and streams by 2025.