In short:
The carcass of what environment authorities say is a dwarf sperm whale has been found washed up on an Adelaide beach.
A local tour boat operator says he saw the same animal two days ago, and has described its death as a "complete mystery".
What's next?
The environment department says National Parks and Wildlife Service staff are working out "how best to deal with the carcass".
The carcass of a "very rare" whale has been found washed up on an Adelaide beach, with a local tour boat operator saying the cause of death appears to be a "complete mystery".
The whale was found at West Beach early on Saturday, and is estimated to be more than two metres in length.
The Department for Environment and Water said the animal was a dwarf sperm whale, a species that is considered rare in Australian waters.
The carcass is estimated to be about two-and-a-half metres long. (Supplied: Temptation Sailing)
John Dundon from the Save West Beach Sand group said beach walkers had made the "distressing" and "very sad" discovery on Saturday morning.
"It's about two-and-a-half metres long, it's a bit bigger than a normal-size dolphin," he said.
"There don't seem to be a lot of signs of thrashing around … where the deceased animal was, so you suspect it's actually died in the water and washed ashore with the tide.
"[Marine authorities are] down here, they've hoisted it up onto the ute and hopefully they're driving it away to conduct a thorough investigation into the cause of the loss of life."
Tour boat operator William Pyke said he had seen the whale on Thursday when it was alive and about four kilometres offshore.
An image of what is believed to be the same whale days before it washed up onshore. (Supplied: Temptation Sailing)
Mr Pyke was with a tour group looking for dolphins when he noticed "an interesting object through the binoculars", which he initially thought was a seal, but turned out to be a whale.
"It had a dorsal fin so we knew it wasn't a seal," he said.
"They're a very rare species — this is the third-ever live sighting in Australia, so it goes to show how rare they are.
"It drew quite a lot of attention in the scientific community."
Mr Pyke said when he found out a whale had washed up, he went to West Beach and inspected the animal's fin.
"The fin's made of cartilage so if they get a nick or a notch … then that's how you can identify individuals, so we compared an image that we took from the boat two days ago to what the specimen looked like washed up ashore, and the markings were the same," he said.
"It didn't seem like there were too many lacerations [but] there were apparently some on the underneath of the animal, there was some blood."
Marine authorities hoisting the carcass onto the back of a ute. (Facebook: Save West Beach Sand)
Mr Pyke said it was possible the animal was sick or had become "disorientated in shallow water".
"They're doing the necropsy now so they're actually going to be able to really tell exactly what has happened and how it has passed," he said.
"It is a complete mystery. Hopefully they'll be able to find out."
An environment department spokesperson said National Parks and Wildlife Service staff had visited the beach to "inspect the carcass and are working with other authorities on the next steps".
"The death of marine mammals, while unfortunate, is not an uncommon occurrence," the spokesperson said.
"There is no evidence to link the whale's death to the dredging trial, which was conducted between October and November 2024."
But Mr Dundon said any such link should not be ruled out, especially in light of another recent marine death.
"We have recently, in December, had the death of a dolphin that washed up at Brighton," he said.
While the department says there is no evidence the death is linked to dredging, John Dundon says such a possibility should not be ruled out. (ABC News: Che Chorley)
Mr Pyke said he was aware of an Indo-Pacific bottlenose dolphin that had "washed up around Grange a couple of weeks ago".
He said he was not convinced that the dredging "would have had an impact" on the whale, but added that it was "really hard to say".
He suggested noise pollution was another factor to consider.
Last month, an animal believed to be a beaked whale was found beached at American River on Kangaroo Island.
An environment department spokesperson said anyone who discovered a dead, sick or stranded marine mammal should "contact their local National Parks and Wildlife Service office or marine wildlife rescue organisation".
"The public is reminded not to interfere with marine mammals, which can carry infectious diseases that can pass between themselves, humans, and their pets," the spokesperson said.