Byron Shire Council is preparing to open the mouth of Belongil Creek on Thursday (1 July).
It comes after an excavator this week scraped back the sandbar which is stopping the creek flowing into the ocean, in the hope the creek would open by itself.
This did not happen and the sandbar continues to act as a dam, not allowing water to escape and causing inundation in some areas of the floodplain.
The water level in the Belongil is currently very high (1.32m) and rainfall predicted this week will increase the risk of flooding the catchment.
James Flockton, Council's Infrastructure Planning Coordinator, said manually opening the creek is a last resort as it increases the risk of a fish kill.
"Belongil Creek, and nearby Tallow Creek, are extremely sensitive ecosystems and while our responsibility is to manage these waterways to mitigate flooding in the catchment, our aim is to have as little impact on the environment as possible," Mr Flockton said.
"One of the big problems is that when a sandbar is opened there is often a very fast release of water from the creek and this can cause a fish kill," he said.
The higher the water level gets behind the sand bar, the greater the risk of flooding in the catchment.
"Allowing the water to continue to build up behind the sandbank and spread across the floodplain means the water is poor quality because of decomposed vegetation like grass and this then flows quickly down the creek and also increases the risk of a fish kill," Mr Flockton said.
"We are hoping that the wet weather will help reduce the chance of a fish kill – that's the last thing we want to see," he said.
Belongil Creek and nearby Tallow Creek are ICOLLs, intermittently open and closed lagoon systems.
Council has been continuously monitoring the water levels and is in regular communication with authorities including the NSW Department of Primary Industries and Environment and the Marine Parks Authority.
"We have communicated to all agencies to let them know we are going to open the sandbar," Mr Flockton said.
Tallow Creek is also closed to the ocean and staff are closely monitoring water levels, the sandbar and rainfall predictions.
Information about Tallow Creek and Belongil Creek is on Council's website.
