Whanganui District Council received a guilty verdict to discharging human waste into a stream.
It is one of five prosecutions taken by the Manawatū-Whanganui Regional Council - three have ended in guilty verdicts and two others are still pending.
The head of regulation for the regional council, Nic Peet, said the charge related to a discharge of wastewater from a pumping station into the Mowhanau Stream in January last year.
On Friday Whanganui District Council chief executive Kym Fell accused the regional council of grasping at straws, saying the legal action had achieved absolutely nothing.
“The fees in defending the litigation have cost our community in excess of $100,000; money which could have been better spent on core services and meaningful environmental improvements.”
Landmeats New Zealand has also been prosecuted for discharging wastewater into the Whanganui River in March last year.
Dr Peet said the discharge was draining into Lake Koputara, a habitat for threatened species.
And earlier this week, Le Poulet Fabuleux Limited was fined $57,000 in the Palmerston North District Court over wastewater from a Himatangi chicken-rearing operation.
Read more about the decision here.
