Recreational swimming in the Tamar Estuary near Launceston may never be safe again under Australian guidelines, says a scientist.
In the past residents of Launceston and surrounds could enjoy the waters of the Tamar Estuary with sand imported to create a beach at Royal Park.
Swimming was deemed unsafe due to a high level of pathogens in the water and could never be safe again for other reasons.
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In the '90s pathogen levels in the yacht basin were measured at 3.8 million enterococci per 100 ml. Now they are measured at significantly lower levels thanks to a variety of improvements in waste water and sewage infrastructure around Launceston.
Enterococci levels are an indicator of the amount of faecal matter in the water.
Tamar Estuary and Esk Rivers program manager Dr Jo Fearman said it was unrealistic to think the estuary would be a viable swimming location near Launceston.
She said the make up of the estuary wasn't conducive to recreational swimming.
"The natural features of the estuary, like tidal mudflats and turbid water, make it less safe to swim there," Dr Fearman said.
"It's location near a densely populated urban area means that when it rains, flows from the catchment and stormwater from the city increase pathogens and impact on water quality."
The National Health and Medical Research Council recommend swimmers have firm ground to enter the water and are able to see the bottom at safe swimming locations.
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Due to the mudflats and silt which is found in the Tamar Estuary neither of these guidelines will be able to be met.
Then there is the fluctuating pathogen levels found in the water after rainfall events. Due to Launceston's combined sewage system the level of pathogens in the water rises after it rains.
The combined system means that sewage and stormwater is flushed into the estuary when it is over capacity.
TasWater in conjunction with the State government and the City of Launceston Council are in the process of upgrading the combined system to increase its capacity.
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Dr Fearman said due to the combined system it was recommended people don't swim in the river for three days after a rainfall event.
"Pathogen levels in the Tamar estuary near Launceston vary over time and are usually elevated after rain. Rainfall brings pathogens downstream from the rivers and also from the urban environment which all meet in the upper estuary," she said.
"Pathogen levels are regulated by Tasmanian regulations, which say that pathogen concentrations below 140 enterococci per 100mL of water is safe for swimming.
"Recently, enterococci levels have exceeded the public health guidelines in about a third of samples taken during monthly sampling of enterococci in the upper estuary, but testing doesn't always coincide with rain. Rain events are being monitored this year to look at the changes in enterococci when it rains."
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