Bubbling brown-green sludge sitting on the top of the Tamar at George Town has so far confounded investigators.
The sludge, just minutes from the main street of George Town, has caused authorities to take note of a potential environmental threat.
The sludge, which authorities remain unsure of its categorisation, was first posted on social media on Tuesday morning, but it was not until The Examiner investigations that the George Town Council, TasWater and the Environmental Protection Agency say they were alerted to it.
Photos of the sludge show a dead seagull floating among it, and the person who posted the photos, who wished to remain anonymous, said they saw at least three others in the area. It was unclear if any fish were also dead in the area.
George Town Council mayor Greg Keiser said an Environmental Health Officer was tasked with investigating the source of the sludge, and by Wednesday afternoon a sample of it had be sent to a laboratory.
He said preliminary investigations showed the sludge was "unlikely to be effluent".
A TasWater spokesperson also confirmed they had carried out investigations into its cause, but maintained those investigations had showed a sewerage pipe close to the sludge did not have any leaks.
"We don't believe the sediment ... came from our infrastructure. The site is now clear," they said.
An EPA spokesperson confirmed the organisation had not been alerted to the potential pollutant, but was in the process of commencing investigations.
"An EPA Incident Response Officer will visit the site this afternoon (Wednesday) to collect some samples," they said.
It was understood investigations into potential pollutants of waterways were an EPA or TasWater responsibility as opposed to a Primary Industries, Parks, Water and Environment responsibility, provided there was not a significant impact to wildlife.
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