A dairy farming leader questions the need for the National Party's proposal to make fencing off waterways compulsory.
A new dairy industry clean streams accord signed last year aims to have all dairy cattle excluded from waterways by 2017.
National's water policy takes that a step further by making it mandatory.
Federated Farmers dairy chair Andrew Hoggard pointed out that most dairy farmers had already done that under the industry accord, and he questioned the need to regulate it.
"So by the exact same date, dairy farmers who supplied the dairy companies that signed the accord will have to have done that. So all of them bar Westland had agreed to that. I believe something like 90 percent of the area to be fenced has already been fenced, so the job was pretty well in hand."
National said it would also spend $100 million over 10 years to buy and retire selected areas of farmland next to important waterways to create an environmental buffer zone
Irrigation New Zealand has given National's water policy the thumbs up, but the Green Party has dismissed it as an election Band Aid, because it said it doesn't address the main cause of water pollution: intensification of land use.