A failure at a wastewater treatment plant in the Hobart's north — caused by a discharge from a chocolate factory nearby — will mean Hobartians have to go much further afield for a swim in the lead-up to Christmas.
'Do not swim' advice remains in place for the River Derwent between Austins Ferry and Old Beach in the North, and Sandy Bay across to Howrah in the south.
TasWater and the Environment Protection Authority (EPA) are working to resolve the incident, which involved a discharge of "sugary water" into the river, which overwhelmed and killed bacteria in a downstream treatment plant this week.
In the meantime, here are the key details you need to know.
Swimmers in the water at Long Beach, Sandy Bay, yesterday. (ABC News: Ebony ten Broeke)
How did this happen?
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Over the last three weeks, TasWater had been working with Cadbury's parent company Mondelez International in disposing its trade waste while its pre-treatment plant is upgraded.
During that time, TasWater noticed a deterioration in the bacteria or "bugs" needed to treat waste at its treatment plant at Cameron Bay, just under 2 kilometres from Cabury's factory.
"We were working closely with Mondelez to make sure that the discharge wouldn't damage the bugs," TasWater general manager Matt Balfe said.
This week, the Cameron Bay Sewage Treatment Plant received "a big spike of sugar" from the Cadbury factory, killing the bacteria and rendering the wastewater entering the River Derwent "incompletely" treated — and a risk to human health.
Have there been problems with the Cadbury factory before?
Right-to-information documents reveal the Cadbury factory released a noxious gas, hydrogen sulphide, at levels 10 to 15 times above the high-risk exposure limit into the surrounding area of Claremont in July.
In an internal email, a TasWater technical services lead wrote that the results of a report assessing the incident "are shocking, to be blunt".
"The whole hill reeks of the gases and this is likely substantially impacting local residents," the email read.
The gas was caused by a build-up of dairy product in pipes, generating toxic waste.
There have been several environmental incidents at the Cadbury factory in Claremont. (ABC News: Scott Ross)
Mondelez International was issued a notice to immediately stop discharging trade waste, until the pipes were cleaned, and the gasses were dispersed through venting.
TasWater received contractual guarantees from Mondelez International that such an incident would not occur again.
When and how will the problem be fixed?
In a statement on Saturday, TasWater general manager operations Brendan Windmeyer said the utility had "began reseeding the Cameron Bay Sewage Treatment Plant with the bacteria required for treatment … trucked in from our Blackmans Bay plant".
"Our team will continue to work around the clock to get the plant fully back up and running as soon as possible," he said.
Tasmanian Environmental Protection Authority director Wes Ford said the effluent will clear from the River Derwent in a matter of days — once the wastewater treatment facility is functional.
"It'll take a few days to stabilise … it will take a few more days after that to be fully functional," Mr Ford said.
"We would expect to see the wastewater treatment plant fully operational in potentially a week."
Next, the remaining effluent will need to disperse.
"We would expect to see that the water quality of the river will improve a few days after the wastewater treatment plant is fairly operational," he said.
The Department of Health says advice will be updated once water testing is completed to confirm the safety of swimming sites.
What are the health risks?
The Department of Health has advised that swimming in contaminated water can cause health issues such as gastroenteritis (diarrhoea or vomiting) and infections of the skin, ears or eyes.
It says to avoid activities that involve "full immersion" in the water.
The EPA says the discharge from the Cadbury factory is "a breach of the trade waste regulations that they operate under". (Tyne McConnon)
What if I've already swum in the River Derwent?
Don't panic.
The Department of Health points out that people can be exposed to germs and viruses any day, although exposure to contaminated water does slightly increase the risk of getting sick.
If you, or someone in your care, have symptoms and are concerned, contact your usual healthcare practitioner or call healthdirect on 1800 022 222 for advice.
Who is at fault?
Loading...At this stage, it remains unclear.
Mr Ford says the discharge of the effluent into the River Derwent constitutes a breach of regulation.
"A discharge of untreated effluent, or partially treated effluent into the Derwent River is a breach of TasWater's discharge arrangements," he said.
"But similarly, a breach of the trade waste discharge from the Mondelez Cadbury Claremont factory is also a breach of the trade waste regulations that they operate under, where TasWater is the regulator."
Mr Ford says the EPA and TasWater have both begun investigations under their respective regulations.
"Those investigations need to take their full course before we can comment further on the outcomes of the investigation," he said.