DNA analysis shows most seawater contamination is caused by sewage,which can leak into stormwater under heavy rain or due to ageing wastewater mains. Water quality monitors regularly test samples from swimming sites across the city for enterococci bacteria.
“Enterococci are a good indicator of faecal contamination in the environment because they shouldn’t be there naturally,they’re found in the human gut,” said Professor Justin Seymour,leader of the Ocean Microbiology Group at the University of Technology Sydney.
Seymour has worked with Beachwatch using DNA analysis to identify exactly where contamination is coming from;enterococci is also found in dogs,birds,wildlife and livestock.
“This is useful because it can guide remediation,” he said. “Do we need to fix a leaky sewage pipe? Or is[the pollution occurring] because we’re seeing a lot of seagulls in a certain region?”
DNA testing at Terrigal Beach,which was often rated “poor” in Beachwatch’s annual water pollution report,confirmed the contamination was caused by sewage,for example.
That spurred the Central Coast Council to investigate 115 kilometres worth of sewage mains. They found one third of the mains required repair.