A wastewater plant owned and operated by Palmerston North City Council has repeatedly breached permitted levels for the discharge of pollutants into the Manawatu River.
A Manawatu-Whanganui Regional Council report shows levels of phosphorus and e-coli exceeding limits in more than half of all water quality tests conducted since the plant opened in 2003, Radio NZ reports.
Ten out of 24 tests on water taken from the Manawatu River fail to reach the consent requirements.
Palmerston North Mayor Jono Naylor says there is no need to reveal the information until the breaches are clarified.
He says the council is still trying to determine whether or not it has in fact breached its consents.
Regional council chairman Bruce Gordon says the city council will not face a financial penalty for the breaches because there is no benefit in that and they don't want to hurt ratepayers.
But city councillor Chris Teo-Sherrell says it's unfair if they're not punished.
"If some measures aren't taken, our officers continue to seemingly take this issue not seriously," he told Radio NZ.
He says the Manawatu River is severely polluted.
"It's like a clear river bed upstream, and downstream it's like a little forest of algae growing all over the riverbed.
"It was just appalling."
NZN