A combination of seaweed and exposed mudflats during an extreme low tide along the coastline between Werribee South and Altona Meadows is the likely cause of an increase in odour reports to Environment Protection Authority Victoria's (EPA) pollution hotline earlier this month.
EPA received about 400 calls from Sunday, 10 January to Friday, 15 January from members of the public complaining of odour, described variously as sewage or seaweed. A majority of the calls came from Melbourne’s westerns suburbs.
EPA Regional Services Executive Director, Damian Wells said officers had been out investigating probable causes.
“EPA officers visited the Werribee Landfill, Ravenhall Landfill and Western Treatment Plant but did not detect any issues that pointed to these sites being the source,” he said.
“EPA also analysed pollution reports against current weather conditions to gain a better understanding of the incident.”
“We found odour was coming from the Werribee and Point Cook areas, however we are unable to pinpoint the exact source.”
“An inspection by EPA’s associate principal odour expert found a large amount of seaweed had washed up on the coastline near Altona Meadows.”
“Low tides had also exposed mudflats containing anoxic sediments caused by years of seagrass build-up and decomposition.”
“After following up on this inspection with our principal marine expert, it is understood that there are significant seagrass and macroalgae communities between Altona Meadows and Werribee South.”
“With the prevailing wind conditions, this part of Port Phillip Bay can often see a large build-up of dislodged seagrass and seaweed (called wrack) along beaches.”
“Decomposing wrack can cause odour and recent higher temperatures would have accelerated breakdown and hence more sulphuric odours associated with increased anoxic conditions.
“Southerly winds may have pushed the odour further inland, which could explain why EPA also received calls from other areas.”
“EPA thanks the community for their help in its investigation.”
“We encourage the community to continue reporting odour concerns immediately to its Pollution Hotline on 1300 372 842 (1300 EPA VIC).”