It is a clause in the licence requirement for the Bowra off-stream storage (aka Bowra Dam) that has been frustrating Nambucca Valley Council for quite some time.
As a transparent system designed to imitate natural flows, whenever there is a rain event like last week's deluge, all the water collected from the catchment must be released and then pumped back into the dam.
General Manager Michael Coulter said this means the council is now required to release about 0.5 metres of the water captured of the 300mm that fell.
"We have difficulty understanding the reason, environmental or otherwise, for this," Mr Coulter said.
"Here we are letting fresh water out of the dam into an already sodden environment and then paying to pump the equivalent volume of water back up.
"I could understand if it was dry but that is not the case. Such rain events are not uncommon and we have to let all that water pass through the system.
"This is not to mention the carbon footprint of the pumping - that is a lot of water to pump, so it is a big pump, a big pipe and a lot of electricity.
"I can't understand the environmental argument for this requirement."
A spokesperson for the Department of Planning, Industry and Environment said the off-river storage was designed as a transparent system, meaning water was pumped into it rather than collected from rainfall.
"Approval of the dam included a requirement for regular releases to mimic natural flows as much as possible," the spokesperson said.
"The storage is in a very small catchment area and, in line with its environmental approvals, rainfall flows through the storage to retain the creek system directly below the dam."