The Derwent Estuary Program has released its 2024 Recreation Water Quality Report which announced that the southern end of Blackmans Bay Beach had been downgraded from Fair to Poor.
Kingborough Mayor, Paula Wriedt said water samples are collected every Tuesday from December to March to inform beach users of the quality of water for swimming.
“Each beach site tested is classified as Good, Fair or Poor for swimming according to the water quality results collated from five years of data,” Cr Wriedt said.
“Water samples are analysed for specific bacteria (enterococci) which indicates the presence of certain types of bacteria in the water which pose a health hazard.
“We have four beaches monitored through the Derwent Estuary’s Beach Watch Program over the warmer months, Taroona, Hinsby, Kingston and Blackmans Bay.
“Both Kingston and Blackmans Bay beaches are broken into 3 testing sections northern, southern and middle.
“The good news is that Taroona Beach has moved from Fair to Good and the northern end of Blackmans Bay Beach is now Good.
“Unfortunately, Blackmans Bay Beach south has been downgraded to Poor with a no swimming advisory being required.
“What this means for beach users is that swimming is not recommend in the southern section of Blackmans Bay Beach, from the large stormwater outfall pipe to the southern cliffs.
“This doesn’t mean the water quality is poor every day at this site, as test results show that 81.5% of our samples over the last 5 years have passed in Blackmans Bay Beach south.
“What we can confirm though, is that water quality at the rest of Blackmans Bay Beach is good for swimming, only the southern end of the beach will have a no swim advisory.
“While we cannot point to the exact cause of the poor water quality results at the southern end, we do know that there are three stormwater outfalls in the area which carry stormwater from around 3000 properties within Blackmans Bay.
“Not only do these stormwater outfalls service most of the homes in Blackmans Bay, but they transport the stormwater off more than 20 km of roads through approximately 60km of pipes, making it a complex system to investigate.
“Now Council is aware that speculation within the community has been raised in the past about the high number of seagulls in the area possibly contributing to the contamination.
“While it’s difficult to absolutely and conclusively rule out the birds as a contributing factor, as enterococci is known to be present in bird faeces. We also have periods of extremely high seagull numbers on the beach and simultaneously very good water quality samples. We also have very poor water quality during times when there are very few, or no seagulls at all.
“Council believes that contaminates entering the stormwater system is the most likely contributor to the poor water quality at this site.
“To and trace the source of contamination Council has taken over 700 additional water sample tests from the beach, waterways, stormwater outfalls alongside over 1000 ammonia tests trying to identify the source.
“Whilst this work is ongoing and we do find and fix different sources of contamination, our investigations haven’t provided a clear conclusive reason as to why this section of beach continues to fail occasionally.
“Water quality at our beaches is important to Council and we will continue to track and trace any contamination, as well as collaborate with our partners to investigate and identify opportunities to improve the water quality in Blackmans Bay south.