Northlake Investments Ltd has this morning been fined $42,500 for discharging contaminants into the Clutha River in August 2017.

The company had denied the charge, brought by the Otago Regional Council, but was found guilty following a one-week trial in Queenstown in April and May.

In sentencing the company in Queenstown this morning Environment Court Judge Brian Dwyer said Northlake had no prior convictions, endeavoured to avoid environmental problems and accepted a submission from its counsel Fletcher Pilditch the offending was an ''aberration''.

While the company had obtained resource consent from the Queenstown Lakes District Council, which included a sediment management plan, it underestimated the extent to which its development would be open and unvegetated that winter.

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Judge Dwyer said, conservatively, 20h of the site was open which was ''unsatisfactory on the basis of its own resource consent documentation''.

"When it became apparent in May 2017 that the site was going to be open over winter ... that should have triggered a re-assessment [of the sediment management plan].

"Northlake must have been aware its site would have been entirely open, unvegetated and [vulnerable] over winter.''

There had been a sediment discharge in July 2017 which was ''indicative of problems upstream'' and two days before the August event Northlake received advice from an engineer about the need for additional silt fencing.

The company, however, did not understand that to be urgent advice and Pilditch said even if it had treated it as urgent and immediately acted on the advice it probably would not have made a ''blind bit of difference'' to the incident which brought them before the court.

Between August 17 and 18 heavy rain ran through a ''natural flow path'' across the exposed Northlake land, conveying sediment-laden water up to 1.5km to the Clutha River.

The discharge, stretching about 500m along the river, was visible for about two days and constituted a breach of the Resource Management Act.

Pilditch submitted there was no deliberateness involved on Northlake's part.

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"It is important for all who are here today to understand that both Northlake Investments and Winton are a group of operators that are committed to undertaking developments of this kind with a no adverse environmental effect approach.''

It had undertaken a ''large number of developments in challenging locations'', for example, close to water, and this incident was a ''total aberration''.

"It's a great shame to the company that this occurred.

"[Northlake development manager Marc] Bretherton was gutted that it took place.''

The company did not wait for a prosecution to resolve the problems and set about to ''immediately take steps to remedy that''.

"They are also a company that makes contributions to the community that they work in and that they operate in, as you would expect from a responsible corporate entity of this kind.

"It took the event extremely seriously.

"It acted and put in a large volume of resource to ensure there was no repetition of this event.

"This is not going to be repeated within this group of companies.

"The message has well and truly been received by the company - they didn't need this prosecution to get the message.''

Along with the fine, to be paid to the regional council, the company was ordered to pay legal costs and disbursements of $2998.60 and witness costs of $417.82.

Civil Construction Ltd was also prosecuted over the discharge - it admitted the charge and in January was fined $25,500.