Green Party water spokesperson Catherine Delahunty says new reports from the Parliamentary Commission for the Environment indicate dairy intensification is causing increasing damage to New Zealand's waterways.
The discharge of pollutants from dairy operations means the water quality of many rivers and streams is continuing to decline.
"While we welcome the good work the Parliamentary Commissioner Dr Jan Wright has done on this report, the findings are grim reading," says Ms Delahunty.
"We would like to see the Commissioner call for a moratorium on further dairy conversions in light of the findings that dairy is causing further deterioration to waterways."
Water quality in New Zealand: Land use and nutrient pollution update report shows that between 2008 and 2012, the Waikato lost 18,700 hectares of plantation forests. Another 28,400 hectares of land became dairy farms. Delahunty says these conversions are illogical, because forests prevent some unwanted substances from leeching off into streams.