PFAS was detected in two trout, an eel and one other fish species from samples taken near the dog park at St Leonards and from near Corra Linn.

Public Health is advising residents to not eat any fish or eel caught from this stretch of the river until further notice as a precautionary measure.

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The news comes less than a week after PFAS was detected at higher than usual levels in the groundwater at the Launceston Airport at a site used for firefighting activities.

Air Services Australia used a type of firefighting foam that contained PFAS for fire fighting activities until 2010. It has since transitioned away from PFAS-containing foam as part of a national response.

While there is yet no hard evidence that suggests PFAS causes any harm to people's health, an international Fairfax Media investigation last year uncovered a potential link between a cancer cluster in the US and PFAS-affected water systems.

Public Health director Mark Veitch advised people should not eat any fish, including eels, caught in the river.

"The levels of PFAS were above the 'trigger level' that indicates the need for further investigation of the source and extent of PFAS in fish in this environment," Dr Veitch said.

"People who have eaten fish and eels from the North Esk to date can be reassured this will not have harmed their health - but as a precaution they should no longer eat them from this area until further notice."

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This section of the North Esk River is already closed to recreational fishing by the Inland Fisheries Service, in accordance with the brown trout fishing season.

PFAS was used worldwide since the 1950s in making countless products such as fabrics, furniture, non-stick cookware and makeup, among other items.

Dr Veitch said so far there had been no link to adverse human health, the chemicals were hard to break down and could accumulate in the bodies of humans and animals.

There is no risk to recreational activity in the area and no PFAS was detected in trout caught upstream towards Blessington.