Horizons Regional Council (HRC) has slapped an abatement notice on Palmerston North City Council (PNCC) for breaching one of 29 conditions on its discharge of treated effluent into the river.

But PNCC mayor Jono Naylor told Rural News he's perplexed by the move. "They are telling us to stop, but they can't tell us what to stop doing."

And the issue appears bigger than just the breach of a single condition of a consent. Farmers, particularly dairy farmers, have long argued they have been hit hard by HRC and that local authorities such as PNCC have been let off the hook for consent breaches. There are suggestions the move by Horizons to issue a significant non-compliance and abatement notice, requiring PNCC to meet its consent conditions by Nov 30, is laced with politics to appease farmers.

While Jono Naylor won't say this directly, he's clearly unhappy with the HRC decision. "Our reading of it is that it's quite possible there are adverse effects on the aquatic life in the Manawatu River as a result of our discharge. But what we believe needs to happen is investigation work to evaluate what the issue is so we can figure out some corrective action to take. We believe an abatement notice at this stage is premature but we are willing to work with Horizons to work out the extent of the issue."

HRC compliance manager Alison Russell says the issue in question had been brought to light following a benthic biota survey which looks at the river's insect life upstream and downstream of the city's discharge.

"There is a significant reduction in the type of insects in the water downstream from the discharge compared with upstream. This is a sign water quality has declined to a point where it doesn't support the same amount of aquatic life as further upstream in a short stretch of the river."

Naylor says PNCC is happy to fix the problem but says it's a complex matter especially when two scientists – one who did the work and another who evaluated the data – disagree. "When you've got two scientists disagreeing, which appears to be the case, I would tend to listen to guy who wrote the report and did the study, and take from it the inferences he believes we should take."

HRC has acknowledged PNCC has always dealt with problems in the past, but cleaning up the Manawatu River is clearly now an emotive as well as a scientific issue.

HRC chairman Bruce Gordon says the matter concerns all involved and must be put right for the sake of the river. "We are focused on achieving this outcome for the community. There is a high degree of public interest in this matter and it's important it is addressed as a matter of urgency."