The Green Party wants a moratorium on new dairy farms and say it's time to start thinking about ways to reduce the number of cows in paddocks.
They're reacting to an official report, released on Thursday, which said rivers and streams were under increasing pressure because of land use.
"Even Minister for Primary Industries Nathan Guy has admitted that there's no room for more cows because of the impact they have on our rivers, lakes and aquifers," primary industries spokeswoman Eugenie Sage said.
"We can do something about it - we can diversify and focus on more arable crops, horticulture, forestry and adding value rather than increasing milk production.
"We can start with a moratorium on new dairy farms, looking at how we can farm with fewer animals on the land, and by instituting a scheme like Ireland's Origin Green scheme, where sustainably produced products attract a premium."