A South Taranaki farmer has copped a $50,000 fine from the Environment Court for letting his effluent tank to overflow for several months.

The Taranaki Regional Council's lawyer Karenza de Silva told the court on Friday that John Campbell Mead's spray irrigation pump - which distributes effluent from a tank onto his land - had failed, causing his tank to overflow and effluent to form in pools across his property from June to October 2015.

"The crown argues it was deliberate, the problems were evident and he must have known about them," de Silva said.

"There was massive potential for adverse environmental effects to occur."

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Mead, who declined a lawyer to represent him, said he had ongoing problems with the pump's switch and had since capped the overflow and removed solid waste from his land.

"I've tried to remediate what I did and have been trying to correct the problem so it doesn't occur again," Mead told Judge Craig Thompson.

"There's no excuse though, I just hadn't been down there in awhile.

"It was unfortunate that it happened but I take full responsibility."

Judge Thompson said the combination of effluent and high rainfall was likely to have resulted in leaching contaminants into ground water.

"There was potential for human and animal health impacts like nitrate poisoning and gastro diseases," he said.

"The dangers of aquifer pollution have been bought home last week."

Over the last two weeks nearly 5000 people in Havelock North in the Hawke's Bay reported symptoms of gastroenteritis, allegedly from drinking contaminated water.

A death in a Hawke's Bay rest home is also suspected to be linked to the gastro outbreak and several schools were closed until further testing could be done on the water bores.

But despite the potential environmental effects, Thompson said he did not believe Mead's offending was deliberate.

"Maintenance was deferred and the easy way out was taken, but he has apologised for that," he said.

"However the time span the offending occurred means this has to be regarded as significant offending."

Thompson settled on a fine of $50,000 to accommodate Mead's early guilty plea and previously unblemished record.

Mead's fine comes close to the largest effluent discharge fine in the region where John Mullan, 64, of Rahotu was fined $66,000 for disposing effluent into groundwater and into a stream on his property.

Director of resource management at the Taranaki Regional Council Fred McLay said Mead's sentencing reflected the seriousness of his actions.

"It emphasises the need for resource users to be aware of and fulfil their obligations to the environment and to the community," he said.