Swimmers are being warned to stay out of the water across a larger section of a popular beach south of Hobart after repeated testing found persistent contamination.
Kingborough Council expanded its no-swim advisory for Blackmans Bay Beach on Thursday to include the middle section.
The advisory now stretches from the southern end of the beach to near the playground, while the northern half remains rated as good for swimming.
The southern and middle sections were downgraded to poor following the 2025–26 sampling program.
The rating is based on five years of data, with just five significant failed samples enough to trigger a downgrade.
The council said the poor rating did not mean the water was unsafe every day, describing each sample as “a snapshot in time”.
Independent investigations found the contamination was most likely entering the stormwater network through leaking or blocked sewer infrastructure.
Possible sources include sewer overflows, infrastructure failures and ageing pipes.
The council says the scale of the network is making the problem harder to track down.
Run-off from more than 3,000 properties and about 20 kilometres of roads travels through roughly 75 kilometres of underground pipes before reaching the bay.
Three of the beach’s four stormwater outfalls are at the southern end, where the water quality problems have been most persistent.
The council said the area also flushed more slowly than many other beaches, allowing contaminants to remain in the shallow southern waters for longer.
The council said it will continue working with TasWater and the Derwent Estuary Program to identify the source and improve water quality.
