Tallow Creek is open and flowing into the ocean with the water level in the creek dropping from 2.42m to 0.52m Monday afternoon (6 December).
Council and National Parks and Wildlife staff noticed a small channel around 8:30 on Monday morning and it continued to get bigger on the outgoing tide.
The water levels in the creek are continuing to change according to the tide, fluctuating between 0.5m and 1.5m AHD.
Chloe Dowsett, Council's Coastal and Biodiversity Coordinator, said staff are monitoring the creek.
Agencies and Council believe the natural opening event has been a success, with minimal fish kill numbers at this stage.
"Fish kills are common occurrences when a creek like this one opens to the ocean and this is normally a result of the very rapid drop in the water level which strips oxygen from the water," Ms Dowsett said.
"The fresh flush of marine water surging up the creek from the large high tides at the moment is great news as this marine water is good for the fish and gives those left in the creek a better chance of survival," Ms Dowsett said.
Tallow Creek is an ICOLL, an intermittently closed and open lake or lagoon, one of 70 in NSW.
The northern part of Tallow Creek is in the jointly managed Arakwal National Park.
Tallow Creek is culturally significant to the Arakwal people and is part of the Cape Byron Marine Park.
