An unexpected spike in poor water quality at Geelong's popular Eastern Beach has triggered a special investigation by EPA Victoria that found the culprits had been lying low at the beach all along.
EPA's Program Coordinator for Beach Report Darren Cottam says the mystery began with three incidents of high bacterial readings in routine water sampling between 28 December and 24 January.
"The results didn't match the usual cause, rainy weather that washes pollution into waterways and the bay from the surrounding land, so we stepped up the sampling regime and called in some help," Mr Cottam said.
EPA took water samples and worked with the City of Greater Geelong to gather information on sources and activities on the waterfront and in the catchment, and Barwon Water ran extra checks of its systems, looking for possible leaks.
EPA also warned the public by issuing a swim advisory, 'SMS alerts, and lowered the daily Beach Report water quality forecast to 'fair' while the investigation continued.
"Back in the office we were looking at more suspects including catchment rainfall, and incidents of high winds or increased wave activity, but there was nothing that pointed to a likely source," Mr Cottam said.
"Eastern Beach has generally good water quality and is often one of the best performing beaches in the bay, so there had to be a hidden factor causing the problem," he said.
"Eventually it was EPA's proactive collection of water samples across the waterfront investigating different potential sources that cracked the case. We had eliminated the likely human causes of raised bacterial levels, and a natural cause became our number one suspect."
The good news is that the source turned out to be a low risk to public health. Sampling indicated that spikes may have been associated with areas of dead, decomposing seagrass and related sediment containing bacteria, which can get resuspended in the water by tides and winds. Seagrass has been linked to spikes of high enterococci in previous years at beaches, such as The Dell at Clifton Springs, Mentone and Altona.
The blackened seagrass can be found on the sand bed or floating in the water at both ends of Eastern Beach.
In the meantime, Eastern Beach has returned to its usual state; the last six water samples have met standards for swimming during dry weather and the forecast has been returned to 'good'.
As a precaution, a water quality alert is still on EPA's website advising beachgoers to avoid coming into contact with blackened, dead seagrass, and water quality monitoring along the Eastern Beach waterfront continued through February.
EPA's daily Beach Report is here epa.vic.gov.au/for-community/summer-water-quality/beach-report
