Enormous, weird fish washes up on an Australian beach. So, what is it?

This is certainly one very fishy encounter.

Two fishers stumbled across quite the surprise when they found a sunfish which had washed onto the beach at Coorong National Park in South Australia.

The photos, taken by Linette Grzelak, were posted on Facebook by National Parks South Australia on Tuesday, and boy, it's a weird looking fish.

Grzelak told CNN they thought the fish was a piece of driftwood when they drove past it.

The strange-looking sea creature has since been identified by the South Australian Museum's ichthyology manager Ralph Foster as an ocean sunfish (Mola mola), due to markings on its tail and the shape of its head.

It's known for its large size, odd flattened body shape and fins, although in this case, Foster estimates the fish to be 1.8 metres (70 inches) long, which is about average for the species.

A species of the sunfish, Mola tecta, was only discovered and named in 2017. It's known as the sunfish because it enjoys basking in the sun on the ocean's surface.

"Researchers have been putting satellite tags and data loggers on these fish and found they will come to the surface and lay on their side on the surface, hence the name the sunfish," Foster explained to the news outlet.

"Once they are warm enough they dive down several hundreds of metres and feed on jellyfish and stay down there for lengthy periods of time."

Foster said very little was known about the sunfish, and it's only in the last few years researchers have known more with the help of technology, especially the Mola tecta.

"Because it had evaded recognition and was misidentified for so long it was named the 'Hoodwinker Sunfish' by its discoverer," he added.

"It was thought to be a purely southern hemisphere species but just a couple of weeks ago one made the news when it turned up on a Californian beach, highlighting how little we know about sunfish in general."

By the way, their size and tendency to sunbake means that boats can hit them, or in much bigger cases, actually sink yachts.

Correction: The Mola mola was not described in 2017, as originally published. It's in fact a genus of the sunfish, Mola tecta, that was newly described that year.