"It's outrageous this should be allowed to occur" within the Arakwal National Park, he said.

James Flockton, flood and drainage engineer for the council, said a build-up of water behind the sand bank had begun to flood residents' backyards. The council has a licence from National Parks and Wildlife Service (NPWS) to open the mouth of the creek when water levels reach 2.2 metres.

The fish kill is caused by the outflow of water with relatively high levels of dissolved oxygen in the centre of the creek. Fish left stranded in the stratified water with poor oxygen levels, however, start to suffocate.

"It's terrible," Mr Flockton said. "It's not something we intended to do."

He said shire staff planned to meet NPWS staff and those from the Cape Byron Marine Park Authority, Crown Lands and Arakwal next week. One option would be for the council to have a more flexible licence to open the estuary, rather than waiting for water levels to reach 2.2 metres.

Loading

The dilemma for the council is to wait for a rain event that would have helped mix the water behind the sand bank. However, if too much rain falls, risks of flooding increase - precisely what the dredging is aimed at reducing, Mr Flockton said.

Mr Pugh said thousands of fish had also died at the nearby Belongil Creek in March, in similar circumstances.

He said it was time for the coastal management plans to be reviewed to ensure further encroachment of properties into the flood zone is restricted.