In late December, under a small footbridge that runs over the Tidal River on the west coast of Wilsons Promontory, Chris Hayward's hand brushed against something troubling.

The river was murky, and Hayward and his Parks Victoria dive team had been largely forced to feel their way along the muddy riverbed. So he wasn't sure he'd found what he feared until he pried the starfish up from the bed and out of the water.

Chris Hayward, Parks Victoria marine ranger, holds aloft the Northern Pacific seastar he fished from the bottom of the Tidal River. Credit:Parks Victoria / Supplied

Its distinctive upturned purple tips were an immediate giveaway. He was holding an Asterias amurensis – a Northern Pacific sea star, and one of Victoria's most-feared marine pests.

"They are voracious – they will eat essentially anything that's not bolted down," says Mark Rodrigue​, Parks Victoria's statewide leader for marine and coasts.