Chief ombudsman Peter Boshier pulled up the council late last year after several "concerning practices" were uncovered while he investigated a complaint into councillor correspondence relating to the Manuherikia River during the last term of council.
Mr Boshier said a councillor deleted an email in 2021 which may have contained official information.
Although the council knew about it, nothing was done to retrieve the communication, he said.
Councillors also said they had "nothing to offer" when asked to co-operate with an official information request "despite possessing evidence seemingly to the contrary", he said.
In his advice to the council, Mr Boshier also listed a councillor using a workplace email other than their council email address to communicate council matters among the concerning practices.
Last week, as a crucial vote on the council’s since-paused land and water plan approached, Cr Kate Wilson provided the Otago Daily Times a letter she wrote to Environment Minister Penny Simmonds.
Cr Wilson, on behalf of four other councillors, appealed to the minister to intervene in the council’s process.
However, her letter did not come from her council email address.
Instead she contacted the minister through an email account linked to another workplace, her farm.
This week, Cr Wilson said there was "nothing sinister" about the email - it was simply written from her personal computer, which used that address.
She was unaware the ombudsman had advised the council this was a concerning practice, she said.
In response, Cr Alexa Forbes called the matter "extremely disappointing".
"I am well aware of process and as a council, we have been well and regularly advised of correct process, so yes, I am aware of the ombudsman’s concerns," Cr Forbes said.
In a span of two weeks before this week’s council meeting, Taieri MP Ingrid Leary filed a series of 45 official information requests relating to councillor correspondence with Ms Simmonds or Resources Minister Shane Jones.
In the House, this week Ms Leary said she believed there was "nothing particularly sinister" in Cr Wilson’s letter, but that it did take her official information requests for it to come out.
In December, Mr Boshier said he discontinued his investigation after the person who made the complaint, former councillor Marian Hobbs, dropped it.
Nevertheless, Mr Boshier noted that when it was asked last year, the council did not say specifically how it was addressing his concerns.
Then, on three separate occasions, including twice last year, his office asked for explanations and records from the council "but unfortunately [that] information was not supplied".
"I am disappointed by the above, and unfortunately as a result my investigation was unnecessarily frustrated and delayed," Mr Boshier said.
Council chief executive Richard Saunders said the council continued to work hard to ensure the organisation met all its statutory requirements under the Local Government Official Information and Meetings Act 1987 (Lgoima).
The council was adequately creating official information as required and was "always open to improving [its] processes".
"Our focus is on transparency, the principle of availability and meeting our responsibilities under the Act."
Procedures had changed since Ms Hobbs’ complaint, he said.
Communication to councillors about what was within scope of an official information request was now much more detailed.
What information was expected from councillors was also provided in much more detail, he said.
"We also have processes in place which are followed to ensure compliance and accountability," Mr Saunders said.
A spokeswoman for the Office of the Ombudsman said the ombudsman encouraged all agencies, including councils, to keep good records and ensure their processes promoted transparency and accountability.
"This includes keeping accessible records of councillor communications, which are subject to request under the Lgoima."
