Taranaki dairy farmers have been fined over water pollution.

A dairy farmer collapsed in the dock and cried into her husband's arms after a judge slapped them with a $45,000 fine for illegally discharging untreated dairy effluent into a Taranaki creek.

John and Alison Vernon, who live and manage a 144-hectare Denbigh Rd dairy farm in Midhurst, admitted one charge each of discharging contaminants into water, a breach of the Resource Management Act.

The offending, which carries a maximum penalty of two years' jail or a $300,000 fine, was discovered after two Taranaki Regional Council (TRC) officers undertook an annual inspection of the farm's effluent system on September 11, 2017.

The officers found untreated dairy effluent flowing into an unnamed tributary of Rum Keg Creek, the Environment Court at New Plymouth heard on Tuesday.

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The discharge came from a hose that had been disconnected from a mobile irrigator after wood chips caused blockages in the effluent pump.

At the time of the offending, approximately 100 cows were being milked on the farm and the TRC estimated approximately 1800 litres of effluent and wash water was being produced each day.

A summary of facts said the officers found a significant discolouration at the point of discharge into the tributary, with discolouration and odour extending for about 400 metres downstream.

The tributary, from which the officers took water samples, flowed for about 2.2 kilometres.

On September 13, the Vernons were served an Abatement Notice requiring them to "undertake works to ensure compliance with Resource Consent".

A re-inspection on September 18 found they had complied.

Defence lawyer Patrick Mooney said the Vernons, who have a history of non-compliance, needed to upgrade their effluent system to enable a greater holding capacity, especially during extreme wet weather, but could not afford to do so.

He said the remorseful farmers were doing what they could to mitigate the runoff and had kept the council informed.

Karenza de Silva, on behalf of TRC, argued the offending had been deliberate.

Environment Judge Brian Dwyer said the offending was "forseeable and inevitable".

He handed down a fine of $60k but gave discounts for prompt guilty pleas, resulting in a combined fine of $45k.

Alison Vernon crumpled as Dwyer delivered his verdict.

Meanwhile, in a separate case, a husband and wife pair of company directors were fined $54,000 after admitting two charges of discharging contaminants into water.

Kevin and Diane Goble did not live at Block 8 Farm, on Block 8 Rd in Waverley, but had employed a contract milker on the site since 2016.

The court heard that an annual inspection by a TRC officer on August 10, 2017 found dairy effluent flowing 40m down a steep bank and into an unnamed tributary of the Moumahaki Stream.

The discharge was noted as "dark coloured and odorous".

The tributary was significantly affected along its entire 2.2km length with water samples showing macroinvertebrate life had been adversely affected.

Dwyer considered the offending as "obvious and careless" and placed it in the most serious category.

He handed down a fine of $80k but gave discounts for an "excellent" past record and prompt guilty pleas, resulting in a fine of $54k.

Following the sentencings, TRC director-resource management Fred McLay said it was disappointing that a small minority of farmers were not operating to the required standards.

"The court has sent a clear message that those who do not take their environmental responsibilities seriously will be penalised," he said.