Opposition parties are expressing shock after Hawke's Bay Regional Council apparently withheld information about the failure of Waihi Dam from councillors.
The council was investigating the dam's failure and regional councillors said yesterday that officials had told them they had received legal advice, but would not give it to them.
A sluice gate at the dam, which belongs to Eastland Group, was damaged last September and not fixed until March, letting silt pour into three waterways for months.
It has cost Wairoa District Council more than $100,000 to clean up the drinking water, and locals say the dam's failure "destroyed" their summer.
RNZ News revealed this week Eastland Group had been breaching its consent for years and the enforcer - the regional council - knew this since 2013, but no penalties were issued.
Labour's environment spokesman, David Parker, said the situation was outrageous.
"Well, I'm astounded, I mean the councillors are the people who are meant to run the show.
"It is the officials who are meant to be accountable to the councillors and it is the latest in a long litany of mistakes that have been made by the people who should have been protecting the people of Wairoa and the river."
Green Party water spokeswoman Catherine Delahunty asked how the people of Wairoa could expect to get answers when the councillors could not.
She said the council was showing an extraordinary lack of transparency in the withholding of information.
The regional council said it was not appropriate to comment while the investigation was under way.