Researchers at the University of Newcastle have found that human faecal contamination from septic tanks in the Tilligerry Creek area is now low.
Part of Tilligerry Creek was closed in 2005 to oyster harvesting due to the discovery of human viruses in oyster meat, and failing septic systems in areas around Salt Ash and Bob's Farm were identified as contributing to the faecal pollution of the estuary.
The University's researchers have conducted two studies over the past 12 months, one to determine if septic systems in an unsewered catchment were still contributing to contamination, and the other into water quality in general and the likely sources of contamination reaching the estuary.
"In the first study, we monitored ground and surface waters in the unsewered Michael Drive subdivision adjacent to Tilligerry Creek for six months and our samples showed no human faecal contamination," lead researcher, Dr Phillip Geary, said.
"We found that the majority of faecal contamination was coming from other sources such as agricultural activites and some from domestic pets.
"Groundwater was not found to be a likely transport pathway for contaminants although surface waters which quickly enter the estuary through a network of open drains do carry faecal contamination.
"In the second study, we sampled 21 sites after heavy rainfall to determine the water quality in affected reaches of Tilligerry Creek.
"Of the 21 sites in the catchment, only six had indicators of human waste present but the levels were extremely low, relative to agricultural sources, particularly herbivores."
Dr Geary said the University research projects had been able to determine that on-site wastewater systems in this part of the catchment were not contributing contaminants to the estuary. Recent testing of the oysters also confirmed the improvements to estuary water quality as human viruses had not been detected in oyster meat.
The research was conducted by members of the School of Environmental and Life Sciences and the Tom Farrell Institute for the Environment, at the University of Newcastle.