The council has discovered four dams in Otago in the past 12 months that have been built illegally.
Council environmental engineering and natural hazards director Gavin Palmer said it had become apparent that Otago was contributing to a serious nationwide problem, where people were building dams without consent under the Resource Management Act (RMA), the Building Act, or both.
Council resource management director Selva Selvarajah said illegal dam construction posed safety and environmental considerations.
The leaky building catastrophe showed what could happen when people did not follow correct building and consent procedures, he said.
"We will not tolerate the construction of unauthorised dams.
Dams can create a variety of hazard risks, therefore if people continue to flout the law with unauthorised construction we will take legal action."
Of the four discovered in Otago, one was in North Otago, one in Queenstown Lakes District and two in the Central Otago area.
Three were on farms and the fourth on a ski-field.
The three farm dams had significant deficiencies and involved not only farm owners and managers but contractors and professional engineers, he said.
In one case, the council was considering taking legal action.
Dr Palmer said that under the Building Act, dams which were 3m high and had a 20,000cu m holding capacity needed building consent.
This was still the case, despite the Department of Building and Housing working on amending the current national dam safety scheme.
There was a "widespread misconception" that dam construction could be legalised retrospectively under the Act. However, there was no certainty that a certificate could or would be issued, he said.
A certificate of acceptance could only be issued if an appropriately qualified engineer was satisfied, based on clear evidence, as to the dam's structural integrity.
"People's actions are negligent if they don't check whether their dam has consents or not. In the interests of safety we will pursue legal action in cases of negligence," Dr Palmer said.
Where there was some doubt about a dam's structural integrity or standard, a landowner might be required to pull the dam down.
Landowners who did not get a consent before contracting out a dam project risked paying more than double what they would have, had they followed the correct legal process in the first place.
"Even though a dam doesn't need RMA consent because it's not built on a waterway, it was still classed as a building and needs Building Act consent."
People should check out the RMA and the Building Act, or seek professional advice when planning a dam, Dr Palmer said.
Dr Selvarajah said that if people were in any doubt about their obligations, they should contact the Regional Council.
