The state’s environment watchdog's confirmed natural coal is behind the deaths of fish in the Anglesea River.

Over 30 fish were found dead in the river last month, the latest in a series of mysterious fish deaths in the region.

Previous incidents have been put down to high levels of acidity in the water.

The EPA’s been looking into the latest problem and says coal from tea tree marshes next to the river caused pH levels in the water to drop.

It says that’s what caused the fish fatalities, rather than pollution or aluminium.

And it says people who find dead or dying fish in or near the river should not eat them.

Picture: Dead fish on the Anglesea River (Anglesea News)