Wairarapa already has a bad track record for polluted waterways and, says a new environmental report, it's probably going to get worse as the dairying industry increases.
The warning comes from a report by Jan Wright, Parliamentary Commissioner for the Environment, which looks at the impact of nitrogen and phosphorus, used as land nutrients, on water quality.
The report found land used for dairy and forestry is projected to grow significantly in the greater Wellington region, leading to more nitrogen getting into swimming spots.
People have already been warned not to swim in Wairarapa rivers such as the Waipoua and Ruamahanga waterways after faecal contamination. The main source of contamination in the Waipoua River is run-off from agriculture and, in the past, it has had toxic algal blooms.
Russell Death, a Massey University associate professor who lives near Dannevirke, says the report clearly illustrates what is already known.
"If we continue with increasing dairy intensification, without some drastic changes in how we farm, the most likely outcome is lose-lose," Professor Death said.
"As the son of a retired dairy farmer and a country lad at heart, I would love to see the win-win for the economy and environment that Jan Wright alluded to in the report."
Kevin Hackwell, Forest & Bird advocacy manager, said nitrogen levels were going to increase in virtually every region even if all dairy farmers employed industry best practice. "What that means is that swimming and fishing in many of our lakes, rivers and estuaries could become a thing of the past, possibly within just seven years.
"What no one wants to talk about is that the current 'white gold rush' is leading New Zealand to a freshwater quality disaster."
Mr Hackwell said resource consents for dairying should be required.
"Restrictions on conversions have already been put in place around Taupo, and now the rate of dairying conversions needs to be actively managed around the rest of the country."
DairyNZ, which represents dairy farmers, said significant work was being done to reduce pollution.
Rick Pridmore, DairyNZ strategy and investment leader for sustainability, said in Wairarapa, all dairy farmers had to meet the targets set in the Sustainable Dairying Water Accord.
He said farmers were committed to fencing waterways, using nutrients efficiently and complying with effluent management regulations.
"We are working openly and constructively with the regional council to help implement the national policy in Wairarapa."
Most of the nitrogen that ends up in fresh water comes from animal urine.
Dr Wright estimates the difference between nitrogen loads in 1996 - when the dairy industry boomed - and in 2020 will increase by almost 20 per cent.
Dr Wright said decision-makers need to be aware of the consequences for the future.