But before it’s decommissioned, council has to figure out what to do with the dam’s 260 megalitres of silt, which is likely contaminated with copper that was used to treat algae blooms.

If it isn’t retired, council will have to maintenance the dam to ensure it meets the NSW safety conditions, which it will be subject to “while ever it holds water”.

Without preempting the investigation, council’s water director Bruce Logan said if the dam, which use to be Barraba’s emergency water supply, wasn’t decommissioned “there may be significant cost to council”.

“I think maybe not decommissioning the full dam, but reducing the size of the wall or put a hole in the wall down to a certain level might be a compromise solution,” Mr Logan said.

While the $100,000 allocated to the investigation might seem like a lot of money, Mr Logan doesn’t “know whether it’s going to be enough”.

“We have to get the silt tested to see what the level of copper is – we’ve received some quotes to suggest that’s $40,000,” he said.

“Depending on what we find there, we are going to have to go to the EPA and ask them under what circumstances they would allow us to decommission the dam and how we should handle the silt. There will be significant costs to work out what we do with that silt.

“If we cut a hole in the dam, that silt will become mobile in the event of a flood – and that’s what the EPA won’t allow to be deposited downstream. If council removes part or all of the dam we have to address what will happen when the silt becomes mobile.”

​Cr Russell Webb said council faced the same problem years ago, when it considered dredging the dam.

“There was a lot of debate about what we would do with it,” Cr Webb said.

“One of the challenges we faced was there was nothing we could do with it, and it would have cost us more to control that problem.”