An international specialist is warning agricultural expansion could result in a "time bomb" effect and the true extent of water pollution might not be realised for many years.
Dr Kevin Parris, of the OECD's Trade and Agriculture Directorate in Paris, is a speaker at an international water pollution conference in Rotorua also attended by the Otago Regional Council, which, jointly with Agresearch, presented a paper on how Otago was dealing with the problem.
Agricultural nutrients were a major pressure on river, lake and marine water quality and nitrogen and phosphorus could sit in soil for a long time before they appeared in water.
"Because of these time lags, in some catchments we won't necessarily see the effects of current farming practices for another 30-40 years," Dr Parris said.
While New Zealand water quality was good in international terms, it was deteriorating, he said.
In 2000, the average for New Zealand was about 35kg of nitrogen per hectare, but by 2008 it was about 45kg per hectare.
However, the average for the 34 OECD countries had decreased 15kg per hectare to 65kg per hectare in the same period.
Further pressure on New Zealand's water quality was expected, he said. Agriculture was a major user of water, and worldwide "we face the enormous challenge of producing almost 50% more food by 2030", he said.
Dr Parris recommended using a mix of policy ideas to address water pollution, including enforcing compliance with water quality regulations and encouraging a co-operative approach in water catchments.
Otago Regional Council environmental information and science director John Threlfall said Dr Parris' comments confirmed that new strategies were needed to cope with further intensification.
"Water quality in Otago is generally excellent, but ORC monitoring has shown some deterioration, especially in the wetter south and west, where intensification has occurred."
Land use changes were also being seen in other drier parts of the region, which would add pressure to new areas, he said.
The regional council had proposed a water plan change, which was intended to maintain good water quality and to improve it where there were signs of land use effects, he said.
"It is very much intended to fit the needs of Otago and differs to much of the rest of New Zealand in that we do not want to control farming practices by issuing consents, but through permitted activity rules."
The council was setting water quality standards for "off-farm" surface water quality, or leachate to groundwater and how the farmer achieved it was up to them.
"These standards will ensure good river water quality and groundwater."
Council staff and Agresearch had presented a paper to the conference outlining some of the changes and the targeted catchment research it had been doing.
"The paper generated a lot of comment and discussion, which is positive feedback that the Otago strategy is a credible alternative to current thinking."
