PLUMMETING salinity has been officially linked to a massive fish kill in the Myall Lakes in recent weeks.
In addition, Department of Primary Industries scientists believe a prolonged stretch of cold weather has combined to increase stress levels of marine life in the estuary.
Many locals also believe pollutants, such as acid-sulphate run-off, could also be affecting water quality.
Following recent Herald reports on increasing public anxiety about the marine park's health, the department confirmed yesterday that testing of dead fish revealed they were suffering from the fungal illness Saprolegniosis, also known as winter disease.
The fungus is different to red spot disease, which is also occurring in the area.
"Commercial fishers have reported seeing more dead fish in the Myall Lakes area, including some that are ulcerated," aquatic biosecurity manager Jane Frances said.
"If caught, fish with severe ulcerations should not be eaten or thrown back."
Low salinity levels, which were recorded at eight parts per thousand last week, also resulted in the suspension of oyster harvesting around Tea Gardens. Harvesting can not resume until salinity levels increase to at least 18 parts per thousand.
The situation is expected to improve over time.
The Herald highlighted yesterday concerns about the ability of the river mouth to flush effectively due to the build-up of sediment on the eastern side of Corrie Island.
A Department of Environment and Climate Change spokeswoman said the department's experts were satisfied enough water was able to pass through the river mouth via the island's north-western passage.
But member for Port Stephens Craig Baumann, who inspected the area yesterday, said the situation needed the State Government's urgent attention.