A stunned fisherman spotted this strange ball floating in the ocean just off the coast of Western Australia.

At first he thought it was a boat, then a fallen hot air balloon.

But when he got closer he realised it was a dead whale whose corpse had become massively swollen.

What is it? At first, Watkins thought it was a boat

Speaking to the West Australian, Mark Watkins, 36, said: “Its stomach was full of gas so it was all bloated up.

“When we got closer we realised it had to be a dead whale because of the smell.”

Mark Watkins was out fishing with his father when they spotted the fallen giantCredit: Facebook / Corey Donohoe

The experienced angler, who was out fishing with his dad south of Perth, had never seen anything like it.

Images Mr Watkins took show the dead whale’s skin is stretched until it appears pink – almost at bursting point.

Some sharks had taken chunks out of the whaleCredit: Facebook / Mark Watkins

As the pair headed back to shore they noticed the whale had deflated as some sharks had bitten chunks out of it.

He added: “We actually did have a 3.5 to 4m white pointer [shark] around our boat that day – it seemed more interested in our boat than the whale.”

Humpback whales are often spotted in the western region of Australia in the summer time.