A failed wastewater treatment plant in Whanganui that plagued the town with a foul stench has been harshly criticised in an independent report.
The plant was built in 2007 but closed in 2013 because of the smell.
Independent reviewer Robert Domm said the Whanganui District Council's management and governance was "entrenched and overly trusting" in the period up to 2005 when the treatment plant was designed.
"The root cause of the failure of the Whanganui Wastewater Treatment Plant traces back to 2003 and 2004 with critical shortcomings in Council's prevailing culture and decision-making processes which allowed endorsement of the plant's radical and flawed design."
The long-running saga has cost Whanganui ratepayers $27 million.
Whanganui mayor Annette Main said the findings of the council-commissioned report were "very damning".
"It talks about a time in local government where, I think it's been described really as 'too cosy' by a previous mayor," she said.
"[It was] too trusting - the relationships were just too tight between between contractors, staff and possibly even the council themselves."
The deliberate withholding of information was astounding, Ms Main said.
"If you go back to look at what councillors were told, they were absolutely misled by the staff," she said.
"It is just very, very disturbing that council staff felt that they just wouldn't bother telling councillors all of the details because they probably wouldn't understand anyway. It is absolutely unbelievable."
The council sued MWH Global for $70m, covering the cost of building the $15m plant which was closed in 2013 and the remainder for a new plant due to be built by 2018.
In February, the council agreed to an out-of-court settlement with MWH Global, which designed and built the failed plant.
The precise terms of the agreement remain confidential.
Whanganui's new wastewater treatment plant, costing $41m dollars, is due for completion in late 2018.