Carbon visible in and around Lake Trevallyn is harmless: TasWater

Launceston Life Saving Club president Geoff Lyons has said that although he didn't know what the sludge was, it had covered most of the lake's surface.

"A lot of it is sunk now, and you can see it on the bottom of the lake, but there's still some around, and I haven't seen it before," he said.

"It's weird stuff."

Mr Lyons said he contacted TasWater on May 22 and registered a complaint online, but had not heard back.

"It wasn't only in Lake Trevallyn," he said.

"It was also lumped up at the South Esk River towards Blackstone Heights.

"At first, I thought it was cow s**t, but there is too much of it to be cow s**t I reckon; it would have to be a powerful lot of sh**ting if it was.

"It could be an overflow from one of the sewerage treatment plants at Westbury or somewhere."

A TasWater spokesperson said:

"We believe residual activated carbon is visible in and around Lake Trevallyn.

"This is a result of a dosing program at our Reatta Road water treatment plant earlier in the year.

"Although unsightly, it is completely harmless.

"The backwash outflow from the Reatta Road water treatment plant travels through a small drainage channel and ends up in Lake Trevallyn, upstream from the boat ramp area.

"This is a normal discharge location for our treatment plant however, because the powdered activated carbon has turned the discharge black, it is now visible.

"Powdered activated carbon (PAC) is commonly used in the water treatment process to filter contaminants.

"At Reatta Road, it was used to remove taste and odour compounds caused by algae present in Lake Trevallyn over the summer.

"PAC is added to the water during the treatment process, and it binds to the compounds, causing both the compound and the PAC to be caught in the filtration system.

"We will continue to monitor this in the coming weeks."

The Examiner asked TasWater how long it would take for the carbon to break up and disappear.

Their spokesperson said to be able to answer this, they would need to "go further up the chain to get an accurate technical response", which would be due in the coming days.