The prosecution followed "numerous complaints" from local businesses and residents of Waharoa through two periods in 2018.
Residents reported that there had been ongoing, persistent and objectionable odour.
We've received quite a few complaints about the bad odour in Waharoa. The odour is from Open Country Dairy, who are well...
Posted by Matamata-Piako District Council on Wednesday, 26 September 2018
In March 2018 the council discovered the odour issues were connected to the failure of the company's wastewater pond liner. As a result, the Waitoa River was also contaminated.
"This is the fifth prosecution of this company, or its predecessor, relating to unlawful discharges into the environment," Lynch said.
"We have the greatest sympathy for the Waharoa community who have to try living with the terrible impacts this stench has caused.
"This large fine sends a very clear message to this company that their operation has to be environmentally sustainable."
The convictions and fine were imposed last week in the Morrinsville District Court by Judge Melanie Harland, who stated that the odour impacts on residents were "profound and, of their kind, serious".
Judge Harland also issued an enforcement order, which the company agreed to, prohibiting further objectionable odour from the site.
The order also requires the company to have a Community Communication Plan to keep the community and council informed of any issues at the plant that may result in objectionable odour being discharged.