The number of dairy farmers badly breaking the rules around polluting waterways has dropped to its lowest recorded level in an audited industry survey.
The DairyNZ survey found 5.8 percent of farms were breaking their resource consents compared to 7 percent two years ago.
But environmental lobby group Forest and Bird says 20 percent of farms in Northland and Auckland are not up to scratch, while the dairy hub of Waikato has such lax monitoring the true extent of pollution is hidden.
The slight drop recorded in the survey coincides with a small rise in the proportion of waterways fenced off, from 94 percent to 96 percent.
DairyNZ said this was all proof its Water Accord to make farms cleaner was working. That was echoed by its catchment engagement leader in Northland, Helen Moody.
"That is just an indication of the attitude that farmers have got now, to saying 'Yip, this is something we want to do, we need to do' - and they are doing," she said.
Ironically, it's Northland that Forest and Bird's Kevin Hackwell has held up as a bad example.
The audited Water Accord figures showed 21 percent of 963 Northland farms significantly broke their resource consent conditions in 2014 and 2015, and Auckland farms were in much the same boat, he said.
"We've had several years now of the sustainable dairy Water Accord and of course 10 years prior to that we had the Clean Streams Accord."
Northland's records had always been consistently high. "It should be well and truly over by now," Mr Hackwell said.
DairyNZ's Helen Moody said the stringent monitoring revealed some farmers were struggling, but monitoring added impetus.
"The Northland Regional Council monitors every farm every year in spring, unannounced, and their level of monitoring has been a big factor in driving dairy farm improvement," she said.
Mr Hackwell also took aim at the opposite approach by Waikato Regional Council: it made pre-announced visits to just 10 percent of farms last year, the lowest of any council despite Waikato having a quarter of all dairy farms. Its rate of significant non-compliance was just 3 percent.
Eight out of 14 regional councils check on all their dairy farms once a year, he said.
"If they were going doing random monitoring or 100 percent monitoring without letting anybody know, I think we would find a very high number."
Up until recently Waikato was monitoring about 25 percent of farms and finding two in every 10 farmers weren't complying, he said.
Forest and Bird wants more farmers breaking the law to be prosecuted.
But Waikato Regional Council said while the significant non-compliance level was low at 3 percent, it caught a lot of farms partially not complying.
Its acting chief executive office and director of resource use, Chris McLay, conceded farm visits were down last year, partly due to staff turnover and IT changes. It also changed its approach to monitoring.
"We used to do helicopter monitoring which got a lot of public attention," said Mr McLay.
It now focused on arranging visits with farm owners and meeting to discuss issues, rather than turning up unannounced.
"We felt if we could get the right infrastructure in place so they could comply 365 days a year, then it would be down to the farmers."
Mr McLay expected farm inspections to rise closer to 25 percent. He will report back to the council in a few weeks on the new approach to monitoring.
The Water Accord report also showed three-quarters of dairy farmers now get information about nitrogen to help gauge pollution, up from 56 percent two years ago.
Shayne O'Shea, who farms on the Mangere River west of Whangarei, said locals there were reaping the environmental rewards.
"We have 19 dairy farms that have riparian edging to the Mangere River. Eighteen of them had had dairy effluent upgrades within the last five years.
"So there has been a huge amount of river fencing and planting and we were awarded fourth equal in New Zealand for water quality improvement last year."
The Water Accord figures are audited. The auditors visited 77 farms to verify what farmers had told dairy companies about such things as their riverbank planting.