Irrigation New Zealand says the Green Party proposal to charge irrigators for water use could cost the average irrigated farm in Canterbury or North Otago $40,000 - $50,000 per year.
The Green Party has launched a plan to clean up waterways which, as well as proposing a charge for irrigation water, also puts forward minimum standards for water quality, water flows and intensive agricultural practice.
It says a charge of 10 cents per 1000 litres would raise up to $570 million a year. Part of that would be used to fund river clean up projects by farmers and councils.
Irrigation New Zealand says the charge suggested would impose a heavy and unfair financial burden on irrigation users.
Chief executive Andrew Curtis says 10,000 litres is the same as applying 1mm of irrigation over a hectare and the average farmer is applying 400 to 500mm of irrigation per hectare each year, depending on the season.
Mr Curtis says that would be a significant cost to farmers and it would mean $40,000 - $50,000 for a 100 hectare farm - the average sized unit in Canterbury and North Otago.
He says the concept is badly thought out and unfair because it would mean irrigation users, most of whom are in Canterbury, would be paying to clean up polluted waterways in other parts of the country.
Federated Farmers' environment spokesperson, Ian MacKenzie, says the organisation supports the aim of the plan to improve water quality and the dairy industry in particular is developing tougher water quality and environmental standards.
But he says there is no direct link between irrigation and water quality deterioration.
Mr MacKenzie also questions the fairness of asking Canterbury irrigators to pay for water pollution problems in other regions.
Minimum water quality standard
Green co-leader Russel Norman says regulations covering pollution from dairy farms are not wide-ranging enough to be effective.
He says resource consents for effluent at present apply only to waste in the dairy shed which represents just 10% of the nitrogen going through a dairy farm.
Dr Norman says a national environmental standard on intensive agriculture would look at stocking rates, fertiliser rates and would vary depending on soil types.
He says it would also cover practices such as keeping stock out of waterways.