yaara: back at the selwyn river, dr. been analyzed, and we'll just see what it comes up as. wow, 9.66 milligrams. that is--that is crazy. the current national policy statement, the limit is 2.4 milligrams. so it's four times that. lan: as alarming as this number is, this is totally typical of virtually all the groundwater and surface water systems that you'll get in this whole area. yaara: dr. joy was part of a group of independent scientists set up by the government to advise it on the reforms. he says the nitrate limit needs to be much lower. mike: it should be 1 milligram. the european union standard is 1 milligram, is the maximum that's allowed in fresh waters, that's the trigger for eutrophication. yaara: eutrophic waterways are often choked with algae and can change oxygen levels, endangering life. mike: the farmers put nitrogen fertilizer on the paddocks to grow grass. what the nitrogen does on the river is it grows algae. algae photosynthesize during the night, they respire, and the oxygen levels drop right down a