Jindalee Road Wines, a wine company in the NSW Wentworth region, and its former manager David Littore pleaded guilty to multiple offences at two separate vineyards between 2016 and 2019.
The company was found to have stolen just under 365 million litres of water - enough to fill about 146 Olympic swimming pools - with a market value of up to $305,000.
The water was secretly swiped from the Western Murray Irrigation pipeline and siphoned off to two properties near NSW-Victoria border.
Different-sized pipes were used to tap into the main water supply and bypass metering equipment.
The illegal pipework was buried underground and allowed unmetered water to be taken and used for irrigation at the properties.
But Western Murray Irrigation detected the set-up after anomalies appeared in routine metre readings.
Further investigations revealed evidence the pipeline had been tampered with and the matter was reported to the regulator in 2020, which launched a prosecution in 2023.
It was the first time a company had been taken to court for breaching sections of water-management law intended to protect supply infrastructure and stop water being taken illegally.
In her judgment on Wednesday, NSW Land and Environment Court judge Sandra Duggan said the offences formed "part of a planned or organised criminal activity" that took place over a long period of time.
"I find that the conduct was intentional, rather than inadvertent or negligent," she said.
"The infrastructure was at such a depth that earth-moving equipment had to be used to uncover it ... this allowed the offending to go undetected for a period."
Jindalee Road Wines was convicted and fined $326,500, while Mr Littore was convicted and fined $172,500.
The defendants have also agreed to pay the regulator's costs of $95,000.
The combined fine for the winery and its former manager is the largest achieved by the Natural Resources Access Regulator (NRAR) since it was established in 2018.
NRAR investigations and enforcement director Lisa Stockley said the court finding was significant for all water users.
"Communities across NSW have said they want a fair, transparent and enforceable water-compliance regime in place to prevent unlawful water take," she said.
"NRAR will take strong regulatory action when required.
"Those who commit serious, substantiated and wilful acts of non-compliance will face the full force of the law."
Jindalee Road Wines has been contacted for comment.
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