A hearing into a major spill that saw thousands of litres of sludge discharged into the Waikato River has been adjourned until July - almost a year after the incident happened.

The Waikato Regional Council has taken the Hamilton City Council and one of its staff to court over a spill that resulted in 90,000 litres of partially treated sewage pouring into the Waikato River last July.

The regional council laid charges in the Hamilton District Court of discharge of sewage in breach of the Resource Management Act earlier this year after senior staff considered the findings of an investigation into the circumstances surrounding the spill.

But it could be several weeks before a verdict is delivered after Judge Harland adjourned the matter to be heard again in July.

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A city council-commissioned report released last year after the spill revealed that almost seven hours passed before the river users group, iwi and public health officials were notified. But council staff had immediately begun a clean-up and containment exercise.

It also showed that water sampling to determine the effects of the spill on the river did not begin until more than two hours after the overflow from a storage tank was discovered by a duty plant technician.

The council has not revealed how widespread the contamination was or how much the clean-up cost, because the matter is now before the court.

The council has not named the staff member involved or disclosed the person's position.

But it said that after an independent investigation, several improvements to the plant's processes - including training of staff - had been recommended.

A staff member said a planned $32 million upgrade at the Pukete wastewater treatment plant would result in "significant improvements".

The Pukete plant treats 45 million litres of wastewater daily.