OPINION: A report this week from the Parliamentary Commissioner for the Environment on land use, nutrient pollution and water quality makes depressing reading.
The commissioner, Dr Jan Wright, finds that, without significantly increased official intervention, a continuing deterioration in water quality is "almost inevitable" as the uses of farmland change in response to economic conditions.
This is going to happen across New Zealand, but Southland and Canterbury are singled out in the report as regions where the problems are particularly pressing.
Anyone with a favourite fishing spot or swimming hole is likely to have seen the effects of this first-hand.
Waters which once ran clear are sometimes now choked with weeds or blighted by slime, boosted by the twin contaminants of nitrogen and phosphorus.
Last summer, ECan warnings about potentially toxic benthic cyanobacteria were issued, at various times and places, for the Hurunui, Ashley, Selwyn, Opihi, Temuka, Pareora, Otaio, and Waihoa Rivers, plus Lakes Ellesmere and Forsyth (Te Waihora and Wairewa).
Perhaps more worrisome is the possible contamination of drinking water supplies by soluble nitrates.
As Ian Shaw, Canterbury University's professor of toxicology, observed on our pages on Tuesday, groundwater is easily affected and nitrates are also "gently making their way to the deeper aquifers".
ECan's 2012 groundwater survey found that 33 wells out of 289 tested - 11 per cent - exceeded safe nitrate levels. Canterbury District Health Board medical officer of health Alistair Humphrey has warned against mixing up baby formula with water from an uncertain source.
Wright's report tries to soften its conclusions with the observation that deteriorating water quality is "not the fault of any one industry alone nor the fault of a single generation", and mentions in passing that industrial wastes and town sewage have a part to play.
But the report in its entirety clearly points the finger at one industry and a relatively short timeframe. It observes that, in Canterbury, the number of hectares given over to dairy farming increased by 122,000 between 1996 and 2008.
The corresponding decrease in sheep and beef farming was 140,000 hectares - the difference can be accounted for by changes in the areas for plantation forests and scrub.
Over the 12 years from 2008 to 2020, a further 100,000 hectares are expected to be converted to dairying. Per hectare, per year, dairy farming releases into the environment more than twice the amount of nitrates of sheep or beef farming.
Farmers, it must be said, are aware of the problem and sloganeering against "dirty dairying" does little to help the situation.
Measures to address pollution include the voluntary Dairying and Clean Streams Accord of 2003 and a Sustainable Dairying Water Accord this year, which some dairy companies say they will enforce as a requirement for collecting milk.
But Wright's report makes clear that in regions - such as Canterbury - where there have been large-scale dairy conversions, "the gains made by increased mitigation are swamped" by the overall increase in nitrogen and phosphorus pollution.
As Wright observes, the dairy sector is our biggest single export earner, and rising costs are driving farmers away from sheep or beef, where there are no corresponding increases in revenue.
Farming is still the backbone of the economy; there is no easy solution to this slowly- evolving crisis.
That is something that every New Zealander - not just farmers - needs to be aware of and grapple with.
Our drinking water is at stake.
- The Press