The Green Party has been criticised for suggesting councils are not prosecuting farmers often enough for polluting waterways.
The party says only a handful of farmers have received infringement notices over the past year for allowing cows into streams and rivers.
Co-leader Russel Norman says nationwide legislation is needed to require farmers to fence off waterways.
But Manawatu-Whanganui Regional Council chief executive Michael McCartney, says although it would adjust its regional plan, legislation is not necessarily the answer.