Authorities are investigating a fish kill event on Sydney's north shore. 

Scores of dead fish and eels have washed up in foam on the banks of Flat Rock Gully Creek, a nature reserve in Northbridge, in the city's north.

Locals reportedly saw plumes of foam being washed downstream before the mass fish kill.

The environmental regulator says an investigation into the “pollution incident” is underway.

“The pollution incident may be linked to firefighting efforts currently being undertaken at a nearby waste facility,” the NSW Environment Protection Authority (EPA) said.

In the days before,  dozens of fire crews had to use foam to attack a blaze that broke out at the Cleanaway Resource Recovery Centre in Artarmon, which was fuelled by large piles of rubbish, including mattresses.

The EPA claims there is “no chance” that PFAS firefighting chemicals were involved in the fish kill.